Using a Reference Number 19
If we don’t know the answer, we can draw two more circles below 8
and 6 and make another calculation. We subtract the 8 and 6 from
10, giving us 2 and 4. We write 2 in the circle below the 8, and 4 in
the circle below the 6.
Th e calculation now looks like this:
(^100) 92 × 94 = 8,600
–8
–6
–2
–4
We now need to calculate 8 times 6, using our usual method of
subtracting diagonally. Two from 6 is 4, which becomes the fi rst
digit of this part of our answer.
We then multiply the numbers in the circles. Th is is 2 times 4,
which is 8, the fi nal digit. Th is gives us 48.
It is easy to add 8,600 and 48.
8,600 + 48 = 8,648
Here is the calculation in full.
(^100) 92 × 94 = 8,600
–8
–6
- 48
–2
–4
8,648 Answer
You can also use the numbers in the bottom circles to help your
subtraction. Th e easy way to take 8 from 94 is to take 10 from 94,
which is 84, and add the 2 in the circle to get 86. Or you could take
6 from 92. To do this, take 10 from 92, which is 82, and add the 4
in the circle to get 86.