Speed Math for Kids Achieve Their Full Potential

How did you go? The answers are:
a) 1.44
b) 1.96
c) 1.68
d) 93.12
e) 9.216
f) 7.5
What if we had to multiply 0.13 × 0.14?
13 × 14 = 182
Where do we put the decimal? How many digits come after the decimal point in the problem? Four,
the 1 and 3 in the first number and the 1 and 4 in the second. So we count back four digits in the answer.
But, wait a minute; there are only three digits in the answer. What do we do? We have to supply the
fourth digit. So, we count back three digits, then supply a fourth digit by putting a 0 in front of the
number. Then we put the decimal point before the 0, so that we have four digits after the decimal.
The answer looks like this:
.0182
We can also write another 0 before the decimal, because there should always be at least one digit
before the decimal. Our answer would now look like this:

0.0182
Let’s try some more:
0.014 × 1.4 =
14 × 14 = 196
Where do we put the decimal? There are four digits after the decimal in the problem; 0, 1 and 4 in the
first number and 4 in the second, so we must have four digits after the decimal in the answer. Because
there are only three digits in our answer, we supply a 0 to make the fourth digit.
Our answer is 0.0196.

Test yourself

Try these   for yourself:

a)  22  ×   2.4 =

b)  0.48    ×   4.8 =

c)  0.048   ×   0.48    =

d)  0.0023  ×   0.23    =

Easy,   wasn’t  it? Here    are the answers:

a)  52.8

b)  2.304

c)  0.02304

d)  0.000529

Beating the system

Understanding this simple principle can help us solve some problems that appear difficult using our
method but can be adapted to make them easy. Here is an example.

8 × 79 =
What reference number would we use for this one? We could use 10 for the reference number for 8,
but 79 is closer to 100. Maybe we could use 50. The speeds maths method is easier to use when the
numbers are close together. So, how do we solve the problem? Why not call the 8, 8.0?