Multiplication Using Any Reference Number 45
3 × 1 = 3
480 + 3 = 483
Th e problem now looks like this:
+3 +1
20 23 × 21 = 24
480
- 3
483 Answer
Checking answers
Let us apply what we learned in the last chapter and check our
answer:
23 × 21 = 483
5 3 15
6
Th e substitute numbers for 23 and 21 are 5 and 3.
5 × 3 = 15
1 + 5 = 6
Six is our check answer.
Th e digits in our original answer, 483, add up to 6:
4 + 8 + 3 = 15
1 + 5 = 6
Th is is the same as our check answer, so we were right.
Let’s try another:
23 × 31 =