ffirs.indd

Standard Long Division Made Easy 153
Remember that these calculations are really only estimates. If you
are dividing by 31 and you make your estimate by dividing by 30,
the answer is not exact—it is only an approximation. For instance,
what if you were dividing 241 by 31?
You round off to 30 and divide by 10 and by 3.
Two hundred and forty-one divided by 10 is 24. We simply drop
the 1.
Twenty-four divided by 3 is 8.
We multiply 8 times 31 and subtract the answer from 241 to get
our remainder.
Eight times 31 is 248. Th is is greater than the number we are
dividing, so we cannot subtract it. Our answer was too high. We
drop to 7.
Seven times 31 is 217.
We subtract 217 from 241 for our remainder.
241 – 217 = 24
So 241 divided by 31 is 7 with 24 remainder.
We could have seen this by observing that 8 times 30 is 240 and
241 is only 1 more. So we can anticipate that 8 times 31 will be too
high.
How about dividing 239 by 29?
We round off to 30 and divide by 10 and by 3 for our estimate.
Two hundred and thirty-nine divided by 10 is 23.
Twenty-three divided by 3 is 7.
But like the previous case, we can see the real answer is probably
diff erent.