ffirs.indd

Checking Your Answers 37
+2
+4
10 12 × 14 = 160
3 5 + 8
168
6
If we have the right answer in our calculation, the
digits in the original answer should add up to the
same as the digits in our check answer.
Let’s try it again, this time using 14 × 14:
14 × 14 = 196
1 + 4 = 5 (substitute for 14)
1 + 4 = 5 (substitute for 14 again)
So our substitute numbers are 5 and 5. Our next step is to multiply
these:
5 × 5 = 25
Twenty-fi ve is a two-digit number, so we add its digits:
2 + 5 = 7
Seven is our check answer.
Now, to fi nd out if we have the correct answer, we add the digits in
our original answer, 196:
1 + 9 + 6 = 16
To bring 16 to a one-digit number:
1 + 6 = 7
Seven is what we got for our check answer, so we can be confi dent
we didn’t make a mistake.