Direct Multiplication 187
63 – 21 = 42
42 × 10 = 420
3 × 7 = 21
420 + 21 = 441
(10 × 7) 7 × 63 420
–3
–7
- 21
–21
441 Answer
Th e calculations were almost identical in this case, but I think the
direct method was easier.
How about 6 × 84?
6 × 80 = 480
6 × 4 = 24
480 + 24 = 504
Now, using two reference numbers, we have:
(10 × 9) 6 × 84 =
–4
–6
–36
Subtracting 36 from 84, we get 480. Four times 6 is 24, then 480 +
24 = 504.
Happily, we get the same answer. Th is time the direct method was
defi nitely easier, although, again, the calculations ended up being
very similar.
Let’s try one more: 8 × 27.