Speed Math for Kids Achieve Their Full Potential

Multiply    by  500.    (Multiply   by  1,000   and divide  by  2.)

514 ×   1,000   =   514,000

Half    of  514,000 is  257,000.    (How    did we  work    this    out?    Half    of  500 is  250 and half    of  14  is  7.)

Multiply    the numbers in  the circles,    and add the result  to  our subtotal.

3   ×   11  =   33

257,000 +   33  =   257,033

Let’s   try one more.

989 ×   994 =

We  use 1,000   as  the reference   number.

Subtract crossways.
989 − 6 = 983
or

994 −   11  =   983

Multiply    our answer  by  1,000.

983 ×   1,000   =   983,000

Multiply    the numbers in  the circles.

Doubling and halving numbers

To use 20 and 50 as reference numbers, we need to be able to double and halve numbers easily.
Sometimes, like when you halve a two-digit number and the tens digit is odd, the calculation is not so
easy.
For example:
78 ÷ 2 =
To halve 78, you might halve 70 to get 35, then halve 8 to get 4, and add the answers, but there is an
easier method.
Seventy-eight is 80 minus 2. Half of 80 is 40 and half of − 2 is −1. So, half of 78 is 40 minus 1, or 39.

Test yourself

Try these   for yourself:

a)  58  ÷   2   =

b)  76  ÷   2   =