3.6 Dividing in different ways
It is very useful to be able to divide in your head. Everyone can learn to develop ways to count in your head or use writing as a help. You need to develop methods that make calculations easier.
Here are a few:
**Dividing by 2**
This usually is easy. You just need to find half of the number.
64 ÷ 2 = 31
288 ÷ 2 = 144
**Dividing by 4**
Here you can think of a “halves’ half”, in other words dividing by 2 twice.
48 ÷ 4 = 24 ÷ 2 = 12
**Dividing by 5**
Here, you can try two different methods.
Multiplying by 2 and dividing by 10:
160/5 = (160 **· **2) ÷ (5 **·** 2) = 320/10 = 32
or
Dividing by 10 and multiplying by 2:
160 ÷ 5 = (160 ÷ 10) **·** 2 = 16 **·** 2 = 32
**Dividing by an added number**
You can factorise the denominator and divide first by one of the factors, and then the other (and then with the third and so forth if you have more than 2 factors).
105 ÷ 15 =
105 ÷ (5 **·** 3)
105 ÷ 5 = 21
21 ÷ 3 = 7
or
105 ÷ 3 = 35
35 ÷ 5 = 7 |