Ratio is a way in which quantities can be divided or shared.
Example
Share £20 between two people in a ratio of 3:1
A ratio of 3 + 1 = 4 parts, the money needs to be divided into 4 parts.
20 ÷ 4 = £5
So 1 person gets 3 x 5 and the other person gets 1 x 5