Multiplication Using Two Reference Numbers 103
Our work looks like this:
(100 × 0.6) 98 × 58 =
–2
–2
–1.2
Subtract 1.2 from 58 to get 56.8. Multiply by 100 to get 5,680.
Multiply the numbers in the circles: 2 times 2 is 4.
5,680 + 4 = 5,684 Answer
Here is the problem fully worked out.
(100 × 0.6) 98 × 58 = 5,680
–2
–2
- 4
–1.2
5,684 Answer
Th e problem above can be solved more easily by simply using a
single reference number of 100 (try it), but it is useful to know there
is another option.
Th e next example is defi nitely easier to solve using two reference
numbers.
96 × 67 =
We use reference numbers of 100 and 70.
(100 × 0.7) 96 × 67 =
–4
–3
–2.8
We multiply 4 times 0.7 to get 2.8 (4 × 7 = 28). We subtract 2.8
from 67 by subtracting 3 and adding 0.2 to get 64.2. Th en we