Stage 2 · Add & subtract strategies
Making 100
Fill up in steps: to the next 10, then 100.
How to do it
Method
Fill up in steps: to the next 10, then 100
63 → 70 → 100: 7 + 30 = 37
Another way
Column subtraction
100 − 63 = 37
In full
63 + ? = 100: fill it up in steps. First to the next ten: 63 → 70 is 7; then 70 → 100 is 30; 7 + 30 = 37. A whole ten goes straight up: 40 + ? = 100 → 60. When the ones aren't 0, check it: the ones make 10 and the tens make 9 (3 + 7 = 10, 6 + 3 = 9). You can also write it as 100 − 63 and subtract in columns with a borrow; the answer is the same.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
30 + ? = 100
Show the answer and working
Answer: 30 + 70 = 100
30 + ? = 100: a whole ten goes straight up, 30 + 70 = 100
Example 2
92 + ? = 100
Show the answer and working
Answer: 92 + 8 = 100
92 + ? = 100: 92 needs 8 to reach 100, 92 + 8 = 100
Example 3
27 + ? = 100
Show the answer and working
Answer: 27 + 73 = 100
27 + ? = 100: fill it up in steps, 27 → 30 is 3, 30 → 100 is 70, 3 + 70 = 73
Example 4
14 + ? = 100
Show the answer and working
Answer: 14 + 86 = 100
14 + ? = 100: fill it up in steps, 14 → 20 is 6, 20 → 100 is 80, 6 + 80 = 86
Practise making 100 in the game →Stage 2 · Add & subtract strategies · Free to start, unlimited questions, no download