Multiplication Using Any Reference Number 53
Our problem now looks like this:
+1
+14
50 51 × 64 = 6,500
3,250
- 14
3,264 Answer
We could check that by casting out the nines:
51 × 64 = 3,264
6 1 6
Six and 4 in 64 add up to 10, which added again gives us 1.
Six times 1 does give us 6, so the answer is correct.
Test you rself
Here are some problems for you to do. See how many you
can do in your head.
a) 45 × 45 = e) 51 × 57 =
b) 49 × 49 = f) 54 × 56 =
c) 47 × 43 = g) 51 × 68 =
d) 44 × 44 = h) 51 × 72 =
How did you do with those? You should have had no
trouble doing all of them in your head. The answers are:
a) 2,025 b) 2,401 c) 2,021 d) 1,936
e) 2,907 f) 3,024 g) 3,468 h) 3,672