Multiplying Decimals 85
Now multiply 32 by 20. To multiply by 20, we multiply by 2 and
by 10.
32 × 2 = 64
64 × 10 = 640
It is easy to add 948,000 and 640.
948,000 + 640 = 948,640
We now have to adjust our answer because we were multiplying by
98, not 980.
Placing one digit after the decimal (or dividing our answer by 10),
we get 94,864.0, which we simply write as 94,864.
Our full work would look like this:
980 × 968 = 948,000
–20
–32
- 640
948,640 Answer
Let’s cast out nines to check the answer.
98.0 × 968 = 94,864
8 14 22
5 4
Five times 8 is 40, which reduces to 4. Our answer, 94,864, also
reduces to 4, so our answer seems to be correct.
We have checked our answer, but casting out nines does not tell
us if the decimal is in the correct position, so let’s double-check by
estimating the answer.
Ninety-eight is almost 100, so we can see if we have placed the
decimal point correctly by multiplying 968 by 100 to get 96,800.
Th is has the same number of digits as our answer, so we can assume
the answer is correct.
1,000