Multiplication Using Two Reference Numbers 93
Easy. Now let’s use 10 and 80 as reference numbers.
+3
(10 × 8) 9 × 83 = 750
–1
- 3
–8
747 Answer
Th ere was not much diff erence in this case, but if you have a large
number to subtract, you may fi nd it easier to choose your reference
numbers so that you end your calculation with an addition.
You could also solve this problem using 10 and 100 as reference
numbers. Let’s try it.
(10 × 10) 9 × 83 = 730
–1
–17
- 17
–10
747 Answer
Th ere are many ways you can use these methods to solve problems. It
is not a matter of which method is right but which method is easiest,
depending on the particular problem you are trying to solve.
Test you rself
Try these problems by yourself:
a) 9 × 68 =
b) 8 × 79 =
c) 94 × 192 =
d) 98 × 168 =