Speed Math for Kids Achieve Their Full Potential

a)  2,345   ÷   36  =

b)  2,713   ÷   25  =

The answers are:

a)  65  r5

b)  108 r13

Working with decimals

We can divide numbers using factors to as many decimal places as we like.
Put as many zeros after the decimal as the number of decimal places you require, and then add one
more. This ensures that your final decimal place is accurate.
If you were dividing 1,486 by 28 and you need accuracy to two decimal places, put three zeros after
the number. You would divide 1,486.000 by 28.

Rounding off decimals

To round off to two decimal places, look at the third digit after the decimal. If it is below 5, you leave
the second digit as it is. If the third digit is 5 or more, add 1 to the second digit.
In this case, the third digit after the decimal is 1. One is lower than 5 so we round off the answer by
leaving the second digit as 7.
The answer, to two decimal places, is 53.07.
If we were rounding off to one decimal place the answer would be 53.1, as the second digit, 7, is
higher than 5, so we round off upwards.
The answer to eight decimal places is 53.07142857.
To round off to seven decimal places, we look at the eighth digit, which is 7. This is above 5, so the 5
is rounded off upwards to 6. The answer to seven decimal places is 53.0714286
To round off to six decimal places, we look at the seventh digit, which is a 5. If the next digit is 5 or
greater we round off upwards, so the 8 is rounded off upwards to 9. The answer to six decimal places is
53.071429.
To round off to five decimal places, we look at the sixth digit, which is a 9, so the 2 is rounded off
upwards to 3. The answer to five decimal places 53.07143.

Test yourself

Try these for yourself. Calculate these to two decimal places:
a) 4,166 ÷ 42 = (Use 6 × 7 as factors)
b) 2,545 ÷ 35 = (Use 5 × 7 as factors)
c) 4,213 ÷ 27 = (Use 3 × 9 as factors)
d) 7,817 ÷ 36 = (Use 6 × 6 as factors)
The answers are:
a) 99.19
b) 72.71
c) 156.04
d) 217.14
Long division by factors allows you to do many mental calculations that most people would not
attempt. I constantly calculate sporting statistics mentally while a game is in progress to check how my