Reception Maths: Finding missing parts
Part of the Reception Maths making and splitting numbers chapter. Chapter overview · whole chapter on one page
Finding missing parts
Tom has 9 stickers. Some are stars and some are hearts. He tells his friend, "Four are stars."
To find the hearts, start with the stars you know. Count on until you reach 9. The number you counted on by is the missing part.
Key ideas
- Start with the part you know.
- Count on to reach the whole.
- The number you counted on by is the missing part.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 9. One part is 4. Find the other part.
- Start with the whole: 9. The whole has all the things.9
- Take away the part you know: 4. What is left is the other part.9 − 4 = 5
- Check by counting on. 4 and 5 must make 9.4 + 5 = 9
- Write the answer. 5
Check. Count on from 4 to 9: 5 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 10. One part is 3. Find the other part.
- Start with the whole: 10. The whole has all the things.10
- Take away the part you know: 3. What is left is the other part.10 − 3 = 7
- Check by counting on. 3 and 7 must make 10.3 + 7 = 10
- Write the answer. 7
Check. Count on from 3 to 10: 7 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Method. Start with 0 and 4. Then move one counter at a time from one part to the other.
- Start with all in one part. Use 0 in one part and the total in the other.0 and 4
- Move one at a time. Each time, one more goes into the first part.4 pairs in order
- Write the pairs. Include 0 and the total.0 and 4, 1 and 3, 2 and 2, 3 and 1, 4 and 0
Check. Each pair adds to 4. ✓
Watch out. Keep a list in order, so you do not miss a pair.
Watch out
Watch out: the missing part is not always the number you see last. Count on from the part you know.
Exam tip
Grown-up tip. Hide one part of a set of cubes with your hand. Ask: “How many are hidden?” Count the visible part, then count on to the whole.
Exercise 4E Finding missing parts
Non-calculatorKey words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 6. One part is 2. Find the other part.
- Start with the whole: 6. The whole has all the things.6
- Take away the part you know: 2. What is left is the other part.6 − 2 = 4
- Check by counting on. 2 and 4 must make 6.2 + 4 = 6
- Write the answer. 4
Check. Count on from 2 to 6: 4 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 9. One part is 5. Find the other part.
- Start with the whole: 9. The whole has all the things.9
- Take away the part you know: 5. What is left is the other part.9 − 5 = 4
- Check by counting on. 5 and 4 must make 9.5 + 4 = 9
- Write the answer. 4
Check. Count on from 5 to 9: 4 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Method. Start with 0 and 4. Then move one counter at a time from one part to the other.
- Start with all in one part. Use 0 in one part and the total in the other.0 and 4
- Move one at a time. Each time, one more goes into the first part.4 pairs in order
- Write the pairs. Include 0 and the total.0 and 4, 1 and 3, 2 and 2, 3 and 1, 4 and 0
Check. Each pair adds to 4. ✓
Watch out. Keep a list in order, so you do not miss a pair.
Method. Start with 0 and 3. Then move one counter at a time from one part to the other.
- Start with all in one part. Use 0 in one part and the total in the other.0 and 3
- Move one at a time. Each time, one more goes into the first part.3 pairs in order
- Write the pairs. Include 0 and the total.0 and 3, 1 and 2, 2 and 1, 3 and 0
Check. Each pair adds to 3. ✓
Watch out. Keep a list in order, so you do not miss a pair.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 7. One part is 3. Find the other part.
- Start with the whole: 7. The whole has all the things.7
- Take away the part you know: 3. What is left is the other part.7 − 3 = 4
- Check by counting on. 3 and 4 must make 7.3 + 4 = 7
- Write the answer. 4
Check. Count on from 3 to 7: 4 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 10. One part is 8. Find the other part.
- Start with the whole: 10. The whole has all the things.10
- Take away the part you know: 8. What is left is the other part.10 − 8 = 2
- Check by counting on. 8 and 2 must make 10.8 + 2 = 10
- Write the answer. 2
Check. Count on from 8 to 10: 2 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Method. Add the two parts in each pair. The right pair makes 6.
- Add the first pair. Check the total.2 + 3 = 5
- Add the other pairs. Only one pair makes the whole.4 + 2 = 6, 1 + 6 = 7
- Write the answer. 4 and 2
Check. 4 + 2 = 6. ✓
Watch out. Add both parts in each pair to check.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 8. One part is 3. Find the other part.
- Start with the whole: 8. The whole has all the things.8
- Take away the part you know: 3. What is left is the other part.8 − 3 = 5
- Check by counting on. 3 and 5 must make 8.3 + 5 = 8
- Write the answer. 5
Check. Count on from 3 to 8: 5 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 10. One part is 6. Find the other part.
- Start with the whole: 10. The whole has all the things.10
- Take away the part you know: 6. What is left is the other part.10 − 6 = 4
- Check by counting on. 6 and 4 must make 10.6 + 4 = 10
- Write the answer. 4
Check. Count on from 6 to 10: 4 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Method. Add the two parts together and compare with 5.
- Count 2. Two things.2
- Add 4 more. Count on four from two.2 + 4 = 6
- Compare with 5. Six is not five.6 is not 5
- Write the answer. No. 2 and 4 make 6.
Check. Count on from 2: 3, 4, 5, 6. Six. ✓
Watch out. Count on all four, not just to 5.
Key words. A missing part is the number we add to the known part to make the whole.
Method. The whole is 9. One part is 4. Find the other part.
- Start with the whole: 9. The whole has all the things.9
- Take away the part you know: 4. What is left is the other part.9 − 4 = 5
- Check by counting on. 4 and 5 must make 9.4 + 5 = 9
- Write the answer. 5
Check. Count on from 4 to 9: 5 more. ✓
Watch out. Count on from the part you know, to reach the whole.
Method. Start with the known part, then count on to the whole.
- Start with the known part. Begin at the part you know.known part
- Count on to the whole. Count on one at a time until you reach the whole.count on to whole
- Write the answer. The number of steps is the missing part.Accept any answer: count on from the known part until you reach the whole. The count is the missing part.
Check. Count on from a part to the whole, and count your steps. ✓
Watch out. Count the steps, not the whole.