# Mental Subtraction

Mental subtraction means taking one number away from another number in your head (without using pen and paper)

Being able to take away numbers in your head is a good skill to learn and will save time

There are a number of different tips and tricks to help with mental subtraction

If you know your number bonds to ten then you will know immediately that

10 - 2 =8

If you know your number bonds to twenty then you will know immediately that

20 - 5 = 15

If you know your number bonds to one hundred then you will know immediately that

100 - 70 = 30

You can learn number bonds to any number - 10, 20, 30, 40, 100, 1,000 etc

### Break Numbers Up (Chunking)

If you are asked to take 36 away from 45 in your head it is much easier to do 45 - 30 - 6

45 - 30 = 15 - 6 = 9

Similarly, 226 - 133 is much easier as 226 - 100 - 30 - 3

226 - 100 = 126 - 30 = 96 - 3 = 93

### Learn to Count Backwards

If you can count backwards in 1's, 2's, 5's and 10's it will help with subtracting

counting backwards in 1's

18 - 5 = (17,16,15,14) 13

counting backwards in 2's

30 - 8 = (28,26,24) 22

counting backwards in 5's

50 - 15 = (45,40) 35

counting backwards in 10's

100 - 40 = (90,80,70) 60