Adding and taking away within 18 · Usually met around P1
Subtracting through ten
Take it down to 10, then take the rest.
How to do it
Method
Take it down to 10, then take the rest
15 − 8 = 15 − 5 − 3 = 10 − 3 = 7
Another way
Take from the ten
10 − 8 = 2, 2 + 5 = 7
In full
15 − 8: first go down to ten, 15 − 5 = 10, then take away the other 3 → 7. Or turn it round: 'eight plus what makes fifteen?' Or take it from the ten: 10 − 8 = 2, 2 + 5 = 7. On paper, it's column subtraction with a borrow. Every way gives the same answer, so use whichever is quickest for you.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
15 − 8
Show the answer and working
Answer: 15 − 8 = 7
Take away down to ten first: 15 − 5 = 10, then 3 more, 10 − 3 = 7
Example 2
15 − 6
Show the answer and working
Answer: 15 − 6 = 9
Take away down to ten first: 15 − 5 = 10, then 1 more, 10 − 1 = 9
Example 3
15 − 9
Show the answer and working
Answer: 15 − 9 = 6
Take away down to ten first: 15 − 5 = 10, then 4 more, 10 − 4 = 6
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