Question

A elevator has a capacity of twenty adults or twenty four childern. How many childern can ride with fifteen adults?

Answer 1

Let adults be x and children be y, then
20x = 24y
x = 6/5y

Let the number of children be a, then
15x + ay = 24y
15(6/5y) + ay = 24y
18y + ay = 24y
18 + a = 24
a = 24 - 18 = 6

Therefore, 6 children can ride with 15 adults.