Julia bought 18 apples at the store. She then divided the apples up between her mother, her father, and herself in 2:1:3 ratio. That is, her mother received 2 parts, her father 1 part, and Julia 3 parts of all the apples. How many apples did each person receive?

Julia bought 18 in total, and she gave each person a number of apples. We can label that number of apples as variable "a", so we say that her mom got 2a, she got 3a and her dad got 1a (so, i. e, her mom got twice as many apples as her dad, and she for thrice as many).

In total, she gave away (to her mom, dad and herself) 2a + 3a + 1a, which is 6a in total. To find how many apples each person got, we have to find the original number of apples ("a"), with the following equation:

6a = 18 (6a is the total number of apples, since she gave away all 18)

Divide the whole eqtn by 6:

a = 18/6

a = 3

Each person got 3 apples, so her dad got 3, her mom 6, and she herself got 9. We can check: 9+6+3=18