Multiplication Using Two Reference Numbers 95
(10 × 49) 9 × 486 =
–1
–4
–49
We subtract 49 from 486. Is this diffi cult? Not at all. We subtract
50 and add 1:
486 – 50 = 436, plus 1 is 437
Multiply the numbers in the circles.
1 × 4 = 4
Th is result is always the fi nal digit in the answer when you multiply
by 9. Th e answer is 4,374. Th e completed problem looks like
this:
(10 × 49) 9 × 486 = 4,370
–1
–4
- 4
–49
4,374 Answer
Th e problems are easy to calculate in your head.
USING FRACTIONS AS MULTIPLES
Th ere is yet another possibility. Th e multiple can be expressed as a
fraction.
What do I mean? Let’s try 94 × 345. We can use 100 and 350
as reference numbers, which we would write as (100 × 3½). Our
problem would look like this:
(100 × 3½) 94 × 345 =
–6
–5