Question

erasers cost $5 per carton and pencils cost $7 per carton. If an order comes in for a total of 15 cartons for $85, how many cartons of each were bought?

Answer 1

let x cartons were bought for eraser and y cartons were bought for pencils
then by the problem
x+y=15
5x+7y=85

Answer 2

multiplying first eq by 5 we get 5x+5y=75

5x+7y=85
(-) 5x+5y=75
______________________(subtracting )
2y=10

hence y=10/2
or y=5
now x+y=15
x=15-y=15-5=10

10 cartoons of eraser were bought and 5 cartoons of pencils were bought