You have a box filled with apples and pears. The ratio of apples to pears is 5:3. You know you have 35 apples, how many pears do you have?
Since you know the number of apples, all you have to do is divide it by its ratio of 5: 35 / 5 =7 . Then you would simply multiply this 7 by the ratio of pears and that will give you the number of pears in the box.
So, 7 x 3 =21 pears. This is because: 35 apples:21 pears = The ratio of: 5:3
