Inside your head you would say:
16 plus 6. . . 22 . . .220 . . .36. . . 256
With practice, you can leave out a lot of that. You don’t have to go through it step by step. You would
only say to yourself:
220 . . . 256
Practise doing this. Saying the right thing in your head as you do the calculation can better than halve
the time it takes.
How would you calculate 7 × 8 in your head? You would ‘see’ 3 and 2 below the 7 and 8. You would
take 2 from the 7 (or 3 from the 8) and say, ‘Fifty’, multiplying by 10 in the same step. Three times 2 is
- All you would say is, ‘Fifty . . . six.’
What about 6 × 7?
You would ‘see’ 4 and 3 below the 6 and 7. Six minus 3 is 3; you say, ‘Thirty’. Four times 3 is 12,
plus 30 is 42. You would just say, ‘Thirty . . . forty-two.’
It’s not as hard as it sounds, is it? And it will become easier the more you do.
Double Multiplication
Let’s multiply 88 by 84. We use 100 as our reference number. Both numbers are below 100 so we draw
the circles below. How many below are they? Twelve and 16. We write 12 and 16 in the circles. Now
subtract crossways: 84 minus 12 is 72. (Subtract 10, then 2, to subtract 12.)
Multiply the answer of 72 by the reference number, 100, to get 7,200.
The calculation so far looks like this:
We now multiply 12 times 16 to finish the calculation.This calculation can be done mentally.
Now add this answer to our subtotal of 7,200.
If you were doing the calculation in your head you would simply add 100 first, then 92, like this:
7,200 plus 100 is 7,300, plus 92 is 7,392. Simple.
You should easily do this in your head with just a little practice.
Test yourself
Try these problems:
a) 87 × 86 =
b) 88 × 88 =
c) 88 × 87 =
d) 88 × 85 =
The answers are:
a) 7,482
b) 7,744
c) 7,656