Year 4: Drawing bar charts and choosing a scale
Part of the Year 4 pictograms, bar charts and time graphs chapter. Chapter overview · whole chapter on one page · Download worksheet (PDF) · Answers (PDF)
Drawing bar charts and choosing a scale
Now it is your turn to draw a bar chart. The data below shows the number of children at four clubs. Follow these steps.
- Give the chart a title that says what it shows. Label the bottom (the clubs) and the side (the number of children).
- Choose a scale. Look at the biggest number. The scale must go a little higher than this. Pick easy steps, such as 2, 5, 10 or 20.
- Draw the bars. Start at 0. Make every bar the same width, with gaps between them. Each bar goes up to the right number on the scale.
How to choose a scale. The biggest number here is 75. If we went up in 1s we would need 75 gridlines, which is far too many. Going up in 10s needs only 8 labels. But 75 is not a multiple of 10, so we put a gridline halfway between the numbers. Each small gap is then 5, and every number (40, 75, 20, 60) lands exactly on a gridline. For small numbers, up to about 10, a scale in 1s is fine. For numbers in the hundreds, steps of 50 or 100 work well.
Key ideas
- Every chart needs a title and labels on both axes.
- The scale starts at 0 and goes a little higher than the biggest number.
- Choose easy steps (1, 2, 5, 10, 20, 50). Add gridlines halfway if some numbers fall between the labels.
- All the bars start on the 0 line and are the same width.
- Always check your chart by reading each bar back and comparing with the table.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 8, 5, 11, 6
Biggest = 11 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 2s to 12: 6 steps, which is a good size.
- Check every number can be shown. Some numbers are not multiples of 2, so they would be between the labels. Put 1 gridline between the numbers so that each gap is 1.2 ÷ 2 = 1
8 = 8 × 1, 5 = 5 × 1, 11 = 11 × 1, 6 = 6 × 1 - Write the scale. The scale goes from 0 to 12 and the labels go up in 2s, with 1 gridline between the numbers (each gap = 1).
Check. The biggest bar will reach 11, which is below the top of the scale, 12. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 40, 75, 20, 60
Biggest = 75 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 10s to 80: 8 steps, which is a good size.
- Check every number can be shown. Some numbers are not multiples of 10, so they would be between the labels. Put 1 gridline between the numbers so that each gap is 5.10 ÷ 2 = 5
40 = 8 × 5, 75 = 15 × 5, 20 = 4 × 5, 60 = 12 × 5 - Write the scale. The scale goes from 0 to 80 and the labels go up in 10s, with 1 gridline between the numbers (each gap = 5).
Check. The biggest bar will reach 75, which is below the top of the scale, 80. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 120, 80, 150, 90
Biggest = 150 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 20s to 160: 8 steps, which is a good size.
- Check every number can be shown. Some numbers are not multiples of 20, so they would be between the labels. Put 1 gridline between the numbers so that each gap is 10.20 ÷ 2 = 10
120 = 12 × 10, 80 = 8 × 10, 150 = 15 × 10, 90 = 9 × 10 - Write the scale. The scale goes from 0 to 160 and the labels go up in 20s, with 1 gridline between the numbers (each gap = 10).
Check. The biggest bar will reach 150, which is below the top of the scale, 160. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
| Pet | Dog | Cat | Fish | Bird |
|---|---|---|---|---|
| Pupils | 8 | 12 | 6 | 10 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 2s: 0, 2, 4, 6...
- Find where each bar stops. Use the scale to find the height of each bar.Dog: 8 is on the line for 8
Cat: 12 is on the line for 12
Fish: 6 is on the line for 6
Bird: 10 is on the line for 10 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
| Day | Mon | Tue | Wed | Thu | Fri |
|---|---|---|---|---|---|
| Books | 35 | 20 | 45 | 30 | 50 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Find where each bar stops. Use the scale to find the height of each bar.Wed: 45 is 1 gap above 40
Fri: 50 is on the line for 50 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
| Day | Mon | Tue | Wed | Thu | Fri |
|---|---|---|---|---|---|
| Visitors | 25 | 40 | 30 | 15 | 35 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Read every bar and compare it with the table. Find the one that is different.
- Find the scale. The numbers up the side are the scale. We must know what one gridline is worth.The numbers go up in 5s: 0, 5, 10, 15...
- Read each bar. Write down the number each bar shows.Mon = 25, Tue = 40, Wed = 20, Thu = 15, Fri = 35
- Compare with the table. The numbers should be exactly the same.Mon: chart 25, table 25 ✓
Tue: chart 40, table 40 ✓
Wed: chart 20, table 30 × (different)
Thu: chart 15, table 15 ✓
Fri: chart 35, table 35 ✓ - Write the answer. The bar that does not match the table is wrong.The bar for Wed is wrong. It shows 20 but it should be 30.
Check. All the other bars match the table. ✓
Watch out. Check every bar, one at a time.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 20s: 0, 20, 40...
Between two numbers there are 4 gaps.
20 ÷ 4 = 5, so each small gap is worth 5. - Find where each bar stops. Use the scale to find the height of each bar.Football: 40 is on the line for 40
Dance: 75 is 3 gaps above 60 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
Watch out
Do not start a bar anywhere but 0. Do not make the bars different widths. And do not change the scale part way up: the numbers on the scale must go up by the same amount each time.Exercise 11D Drawing bar charts and choosing a scale
Non-calculatorKey words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 7, 4, 9, 6
Biggest = 9 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 2s to 10: 5 steps, which is a good size.
- Check every number can be shown. Some numbers are not multiples of 2, so they would be between the labels. Put 1 gridline between the numbers so that each gap is 1.2 ÷ 2 = 1
7 = 7 × 1, 4 = 4 × 1, 9 = 9 × 1, 6 = 6 × 1 - Write the scale. The scale goes from 0 to 10 and the labels go up in 2s, with 1 gridline between the numbers (each gap = 1).
Check. The biggest bar will reach 9, which is below the top of the scale, 10. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 30, 55, 20, 45
Biggest = 55 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 10s to 60: 6 steps, which is a good size.
- Check every number can be shown. Some numbers are not multiples of 10, so they would be between the labels. Put 1 gridline between the numbers so that each gap is 5.10 ÷ 2 = 5
30 = 6 × 5, 55 = 11 × 5, 20 = 4 × 5, 45 = 9 × 5 - Write the scale. The scale goes from 0 to 60 and the labels go up in 10s, with 1 gridline between the numbers (each gap = 5).
Check. The biggest bar will reach 55, which is below the top of the scale, 60. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 150, 100, 200, 250
Biggest = 250 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 50s to 250: 5 steps, which is a good size.
- Check every number can be shown. Each number must land on a gridline. Every number is a multiple of 50.150 = 3 × 50, 100 = 2 × 50, 200 = 4 × 50, 250 = 5 × 50
- Write the scale. The scale goes from 0 to 250 and the labels go up in 50s.
Check. The biggest bar will reach 250, which is below the top of the scale, 250. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the biggest number. Choose easy steps so the scale is not too long, and make sure every number can be drawn exactly.
- Find the biggest number. The scale must reach at least this far.Numbers: 12, 6, 10, 8
Biggest = 12 - Choose a step for the labels. The scale should have no more than about 8 numbers, and easy steps like 1, 2, 5, 10 or 20 are best.Going up in 2s to 12: 6 steps, which is a good size.
- Check every number can be shown. Each number must land on a gridline. Every number is a multiple of 2.12 = 6 × 2, 6 = 3 × 2, 10 = 5 × 2, 8 = 4 × 2
- Write the scale. The scale goes from 0 to 12 and the labels go up in 2s.
Check. The biggest bar will reach 12, which is below the top of the scale, 12. ✓
Watch out. A scale that is too short cuts off the tall bars. A scale that goes up in 1s for big numbers is too long.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. One gap is worth 5. Divide 10 by 5 to find how many gaps high the bar is.
- Write down what one gap is worth. Each gap stands for the same amount.1 gap = 5
- Divide. How many lots of the gap fit into the number?10 ÷ 5 = 2
Check. 2 × 5 = 10. ✓
Watch out. Divide by the gap, not by the step.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. One gap is worth 5. Divide 25 by 5 to find how many gaps high the bar is.
- Write down what one gap is worth. Each gap stands for the same amount.1 gap = 5
- Divide. How many lots of the gap fit into the number?25 ÷ 5 = 5
Check. 5 × 5 = 25. ✓
Watch out. Divide by the gap, not by the step.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. One gap is worth 5. Divide 40 by 5 to find how many gaps high the bar is.
- Write down what one gap is worth. Each gap stands for the same amount.1 gap = 5
- Divide. How many lots of the gap fit into the number?40 ÷ 5 = 8
Check. 8 × 5 = 40. ✓
Watch out. Divide by the gap, not by the step.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. One gap is worth 5. Divide 35 by 5 to find how many gaps high the bar is.
- Write down what one gap is worth. Each gap stands for the same amount.1 gap = 5
- Divide. How many lots of the gap fit into the number?35 ÷ 5 = 7
Check. 7 × 5 = 35. ✓
Watch out. Divide by the gap, not by the step.
| Pet | Dog | Cat | Rabbit | Fish |
|---|---|---|---|---|
| Pupils | 6 | 9 | 4 | 7 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 2s: 0, 2, 4...
Between two numbers there are 2 gaps.
2 ÷ 2 = 1, so each small gap is worth 1. - Find where each bar stops. Use the scale to find the height of each bar.Dog: 6 is on the line for 6
Cat: 9 is 1 gap above 8
Rabbit: 4 is on the line for 4
Fish: 7 is 1 gap above 6 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
| Day | Mon | Tue | Wed | Thu | Fri |
|---|---|---|---|---|---|
| Visitors | 20 | 35 | 15 | 40 | 25 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 5s: 0, 5, 10, 15...
- Find where each bar stops. Use the scale to find the height of each bar.Tue: 35 is on the line for 35
Thu: 40 is on the line for 40 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
| Sandwich | Cheese | Ham | Egg | Tuna |
|---|---|---|---|---|
| Sold | 40 | 70 | 30 | 60 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Find each bar’s height on the scale, then draw bars of the same width up to that height.
- Check the scale. We need to know what each gridline is worth before we draw.The numbers go up in 20s: 0, 20, 40...
Between two numbers there are 2 gaps.
20 ÷ 2 = 10, so each small gap is worth 10. - Find where each bar stops. Use the scale to find the height of each bar.Cheese: 40 is on the line for 40
Ham: 70 is 1 gap above 60
Egg: 30 is 1 gap above 20
Tuna: 60 is on the line for 60 - Draw the bars. Start at the bottom. Draw each bar up to its height. Make every bar the same width, with a gap between the bars.
Check. Read each bar back from your chart: they should match the table. ✓
Watch out. Draw every bar from the bottom axis (the 0 line), with the same width.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the bar carefully and read off the number for Mon.
- Find the scale. The numbers up the side are the scale. Not every gridline has a number, so we must work out what each small gap is worth.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Read the bar for Mon. Find the top of the bar, then look across to the scale (follow the orange dotted line).The top of the bar for Mon is exactly on the line for 30.
- Write the answer. Mon = 30 cakes
Check. Look again at the picture: Mon is 30. ✓
Watch out. Work out what each gridline is worth before you read a bar. The scale does not always go up in 1s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the bar carefully and read off the number for Tue.
- Find the scale. The numbers up the side are the scale. Not every gridline has a number, so we must work out what each small gap is worth.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Read the bar for Tue. Find the top of the bar, then look across to the scale (follow the orange dotted line).The top of the bar for Tue is between 40 and 50.
It is 1 small gap after 40: 40 + 5 = 45 - Write the answer. Tue = 45 cakes
Check. Look again at the picture: Tue is 45. ✓
Watch out. Work out what each gridline is worth before you read a bar. The scale does not always go up in 1s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the bar carefully and read off the number for Wed.
- Find the scale. The numbers up the side are the scale. Not every gridline has a number, so we must work out what each small gap is worth.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Read the bar for Wed. Find the top of the bar, then look across to the scale (follow the orange dotted line).The top of the bar for Wed is exactly on the line for 20.
- Write the answer. Wed = 20 cakes
Check. Look again at the picture: Wed is 20. ✓
Watch out. Work out what each gridline is worth before you read a bar. The scale does not always go up in 1s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the bar carefully and read off the number for Thu.
- Find the scale. The numbers up the side are the scale. Not every gridline has a number, so we must work out what each small gap is worth.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Read the bar for Thu. Find the top of the bar, then look across to the scale (follow the orange dotted line).The top of the bar for Thu is between 50 and 60.
It is 1 small gap after 50: 50 + 5 = 55 - Write the answer. Thu = 55 cakes
Check. Look again at the picture: Thu is 55. ✓
Watch out. Work out what each gridline is worth before you read a bar. The scale does not always go up in 1s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Look at the bar carefully and read off the number for Fri.
- Find the scale. The numbers up the side are the scale. Not every gridline has a number, so we must work out what each small gap is worth.The numbers go up in 10s: 0, 10, 20...
Between two numbers there are 2 gaps.
10 ÷ 2 = 5, so each small gap is worth 5. - Read the bar for Fri. Find the top of the bar, then look across to the scale (follow the orange dotted line).The top of the bar for Fri is between 30 and 40.
It is 1 small gap after 30: 30 + 5 = 35 - Write the answer. Fri = 35 cakes
Check. Look again at the picture: Fri is 35. ✓
Watch out. Work out what each gridline is worth before you read a bar. The scale does not always go up in 1s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Check that the numbers on the scale go up by the same amount each time.
- Read the labels on the scale. Start at the bottom and write the labels in order.0, 10, 20, 40, 50, 60
- Check the gaps. The numbers should go up by the same step each time.0 to 10: +10
10 to 20: +10
20 to 40: +20 (different!)
40 to 50: +10 - Write the answer. The gap from 20 to 40 is too big. The label 30 is missing.The correct scale is 0, 10, 20, 30, 40, 50.
Check. Now each step is +10. ✓
Watch out. The numbers on a scale must go up by the same amount each time.
| Day | Mon | Tue | Wed | Thu | Fri |
|---|---|---|---|---|---|
| Visitors | 25 | 40 | 30 | 15 | 35 |
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Read every bar and compare it with the table. Find the one that is different.
- Find the scale. The numbers up the side are the scale. We must know what one gridline is worth.The numbers go up in 5s: 0, 5, 10, 15...
- Read each bar. Write down the number each bar shows.Mon = 25, Tue = 40, Wed = 20, Thu = 15, Fri = 35
- Compare with the table. The numbers should be exactly the same.Mon: chart 25, table 25 ✓
Tue: chart 40, table 40 ✓
Wed: chart 20, table 30 × (different)
Thu: chart 15, table 15 ✓
Fri: chart 35, table 35 ✓ - Write the answer. The bar that does not match the table is wrong.The bar for Wed is wrong. It shows 20 but it should be 30.
Check. All the other bars match the table. ✓
Watch out. Check every bar, one at a time.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Think how many labels a scale in 1s needs, and what a better step is.
- Find the length of a scale in 1s. The scale must reach at least 90, so it needs a label for every number from 0 to 90.Going up in 1s: 90 labels. This is far too many.
- Try bigger steps. Choose an easy step that gives about 8 labels.Going up in 10s: 0, 10, 20, … 90 gives 9 labels.
- Check the data. The data is between 40 and 90. With steps of 10 each number needs to be on a line.If a value is not a multiple of 10, add a gridline halfway (each gap is 5).
- Write the answer. No, it is not a good idea. A scale going up in 10s would be better.
Check. 9 labels is easy to read. 90 labels is not. ✓
Watch out. Pick steps so that the scale has about 5 to 10 numbers.
| Colour | Tally |
|---|---|
| Red | |
| Blue | |
| Green | |
| Yellow |
Key words. A tally mark is a small stroke we draw for each thing we count. Every fifth stroke goes across the other four, so each group of 5 is easy to see. The frequency is the total number of tally marks in one row. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. First read the frequency from each row of the tally chart. Then draw the bars.
- Count the tally marks. Count in fives, then add the single strokes.Red: 1 group of 5 = 5, and 3 more = 5 + 3 = 8
Blue: 1 group of 5 = 5
Green: 2 groups of 5 = 10
Yellow: 1 group of 5 = 5, and 1 more = 5 + 1 = 6 - Choose a scale. The biggest number is 10. A scale that goes up in 2s with a gridline between each pair of numbers (each gap 1) works well.Scale: 0, 2, 4, 6, 8, 10
- Draw the bars. Draw each bar to the number you counted.
Check. The bars have heights 8, 5, 10 and 6. ✓
Watch out. Count the tally marks carefully before you draw.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. A number can be shown exactly if it is a multiple of 20 (the size of one gap).
- Divide by the size of a gap. If it divides exactly, the number is on a gridline.60 ÷ 20 = 3
- Decide. It divides exactly, so it is on a gridline: yes.
Check. 20 × 3 = 60. ✓
Watch out. Check by multiplying, or by counting in 20s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. A number can be shown exactly if it is a multiple of 20 (the size of one gap).
- Divide by the size of a gap. If it divides exactly, the number is on a gridline.130 ÷ 20 = 6.5
- Decide. It does not divide exactly, so it is between two gridlines: no.
Check. 20 × 6 = 120, which is not 130. ✓
Watch out. Check by multiplying, or by counting in 20s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. A number can be shown exactly if it is a multiple of 20 (the size of one gap).
- Divide by the size of a gap. If it divides exactly, the number is on a gridline.90 ÷ 20 = 4.5
- Decide. It does not divide exactly, so it is between two gridlines: no.
Check. 20 × 4 = 80, which is not 90. ✓
Watch out. Check by multiplying, or by counting in 20s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. A number can be shown exactly if it is a multiple of 20 (the size of one gap).
- Divide by the size of a gap. If it divides exactly, the number is on a gridline.140 ÷ 20 = 7
- Decide. It divides exactly, so it is on a gridline: yes.
Check. 20 × 7 = 140. ✓
Watch out. Check by multiplying, or by counting in 20s.
Key words. A bar chart uses bars to show data. The height (or length) of a bar shows how many. The scale is the row of numbers on the side. It tells you how much each gridline is worth.
Method. Think about what makes a bar chart fair and easy to read.
- Think about the heights. In a bar chart the height (or length) of a bar shows the number. The bars are drawn from the same 0 line.The height tells us the number.
- Think about the widths. If the bars are different widths, it is hard to compare them fairly.The bars should be the same width, with equal gaps.
- Write the answer. No, Zainab is wrong. All the bars should be the same width.
Check. On every chart in this chapter the bars are the same width. ✓
Watch out. Same width, equal gaps, start at 0.