Question

how to do ratio ?

Answer 1

we need a little more information to know what your asking.

example: you bought 4 apples, you ate 2 of them, so you ate 2 out of 4 in other words, you ate 2/4 of them, so you ate 1/2

Answer 2

Ratio is relation existing between any two quatities of same kind.
ratio of two quantities is an absolute number if it has no unit.
ratio is always expressed in lowest terms.