ffirs.indd

168 Speed Math for Kids
Th e answer checks correctly.
If you are not sure how to check a problem in division, try a simple
problem like 14 ÷ 4 = 3 r2.
Reverse the problem, subtracting the 2 remainder from 14 to get
3 × 4 = 14 – 2. Th en apply the method to the problem that you
want to check.
Finding the remainder with a calculator
When you carry out a division with your calculator, it gives your
remainder as a decimal. Is there an easy way to fi nd out the true
remainder instead?
Yes, there is. If you divide 326 by 7 with a calculator, you get an
answer of 46.571428 with an eight-digit calculator. What if you are
trying to calculate items you have to divide up—how do you know
how many will be left over?
Th e simple way is to subtract the whole number before the decimal
and just get the decimal part of the answer. In this case you would
just subtract 46, which gives 0.571428. Now multiply this number
by the number you divided by. For our calculation, we multiply
0.571428 by 7 to get an answer of 3.999996. You round the answer
off to 4 remainder.
Why didn’t the calculator just say 4? Because it only works with
numbers to a limited number of decimal places, so the answer is
never exact.
Multiplying the decimal remainder will almost always give an answer
that is fractionally below the correct remainder. You will be able to
see this for yourself. If you are dividing 326 chairs into 7 classrooms
at school, you know you won’t have 46 in each room with 3.999996
chairs left over. You would have 4 chairs to keep for spares.
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