Year 2: Arrays
Part of the Year 2 multiplying and dividing chapter. Chapter overview · whole chapter on one page
Arrays
An array is a neat pattern of things in rows and columns. The rows go across. The columns go down. Each row has the same number of things.
To find the total, count the rows. Then count how many are in one row. Add that number once for each row.
Key ideas
- An array has rows across and columns down.
- Each row has the same number of things.
- Count the rows, and count the things in one row.
- Add one row for each row in the array.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 2 rows.2 rows
- Count the things in one row. Each row has 5 cubes.5 in each row
- Add the rows. Add 5 once for each row.5 + 5 = 10
Check. Count down the columns too. Both ways make 10. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 4 rows.4 rows
- Count the things in one row. Each row has 3 cakes.3 in each row
- Add the rows. Add 3 once for each row.3 + 3 + 3 + 3 = 12
Check. Count down the columns too. Both ways make 12. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 3 rows.3 rows
- Count the things in one row. Each row has 6 eggs.6 in each row
- Add the rows. Add 6 once for each row.6 + 6 + 6 = 18
Check. Count down the columns too. Both ways make 18. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Watch out
Watch out: count the rows and the things in one row. Do not count the columns and add them to the rows.
Exam tip
Grown-up tip. Lay out buttons in rows on the table. Ask: “How many rows? How many in each row? How many altogether?” Then turn the tray round and count the columns.
Exercise 3B Arrays
Non-calculatorMethod. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 2 rows.2 rows
- Count the things in one row. Each row has 4 biscuits.4 in each row
- Add the rows. Add 4 once for each row.4 + 4 = 8
Check. Count down the columns too. Both ways make 8. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 5 rows.5 rows
- Count the things in one row. Each row has 2 stars.2 in each row
- Add the rows. Add 2 once for each row.2 + 2 + 2 + 2 + 2 = 10
Check. Count down the columns too. Both ways make 10. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 3 rows.3 rows
- Count the things in one row. Each row has 3 balls.3 in each row
- Add the rows. Add 3 once for each row.3 + 3 + 3 = 9
Check. Count down the columns too. Both ways make 9. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 3 rows.3 rows
- Count the things in one row. Each row has 6 pears.6 in each row
- Add the rows. Add 6 once for each row.6 + 6 + 6 = 18
Check. Count down the columns too. Both ways make 18. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 2 rows.2 rows
- Count the things in one row. Each row has 3 bags.3 in each row
- Add the rows. Add 3 once for each row.3 + 3 = 6
Check. Count down the columns too. Both ways make 6. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 4 rows.4 rows
- Count the things in one row. Each row has 2 hats.2 in each row
- Add the rows. Add 2 once for each row.2 + 2 + 2 + 2 = 8
Check. Count down the columns too. Both ways make 8. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 3 rows.3 rows
- Count the things in one row. Each row has 5 books.5 in each row
- Add the rows. Add 5 once for each row.5 + 5 + 5 = 15
Check. Count down the columns too. Both ways make 15. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 6 rows.6 rows
- Count the things in one row. Each row has 2 shoes.2 in each row
- Add the rows. Add 2 once for each row.2 + 2 + 2 + 2 + 2 + 2 = 12
Check. Count down the columns too. Both ways make 12. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. Count the rows. Then add the number in one row, once for each row.
- Count the rows. There are 4 rows.4 rows
- Count the things in one row. Each row has 5 books.5 in each row
- Add the rows. Add 5 once for each row.5 + 5 + 5 + 5 = 20
Check. Count down the columns too. Both ways make 20. ✓
Watch out. Rows go across. Columns go down. Count each row once, and do not skip any.
Method. The array has 3 rows. Share the 15 balls into 3 equal rows.
- Count the rows. There are 3 rows.3 rows
- Share the balls into the rows. Put 5 in each row: 5 + 5 + 5 = 15.5 + 5 + 5 = 15
- Write the answer. Each row has 5 balls.5
Check. 3 rows of 5 make 15. ✓
Watch out. Put one ball in each row at a time, so the rows stay equal.
Method. Work out the total, then compare it with the claim.
- Work out the total. 2 groups of 5: add 5 2 times.5 + 5 = 10
- Compare with the claim. The claim says 10. The total is 10.10 = 10
- Write the answer. The claim is right only if the two numbers match.Yes. 2 × 5 = 10
Check. Count in 5s: 5, 10. ✓
Watch out. Add the same number once for each group. Do not stop early.
Method. Count each array. Compare the totals.
- Count 4 rows of 3. Each row has 3 things, and there are 4 rows.3 + 3 + 3 + 3 = 12
- Count 3 rows of 4. Each row has 4 things, and there are 3 rows.4 + 4 + 4 = 12
- Write the answer. Both arrays have the same number of things.No. Both arrays have 12 things.
Check. Turn one array round and count it again. You get 12 too. ✓
Watch out. Turning an array round does not change how many things there are.
Method. Try to share the 12 counters into 5 equal rows.
- Try 5 rows. Each row needs the same number of counters.12 counters, 5 rows
- Share the counters into the rows. Put 2 in each of the 5 rows. That uses 10 counters.2 + 2 + 2 + 2 + 2 = 10
- Write the answer. There are 2 counters left over, so the rows are not equal.No. 2 are left over.
Check. 10 counters in the rows and 2 left over make 12. ✓
Watch out. If some things are left over, the rows cannot all be the same.