Numbers Above the Reference Number 27
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.
Th e calculation so far looks like this:
100 88 × 84 = 7,200
–12
–16
We now multiply 12 times 16 to fi nish the calculation.
+2
+6
10 12 × 16 = 180
- 12
192
Th is 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 fi rst, 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 you rself
Try these problems:
a) 87 × 86 = c) 88 × 87 =
b) 88 × 88 = d) 88 × 85 =