Question

A corner store sells two kinds of baked goods: cakes and pies. A cake costs $5 and a pie costs $7. In one day, the store sold 15 baked goods for a total of $91. How many cakes did they sell?

Answer 1

let x and y be the no of cakes and no. of pies sold respectively
x+y=15 -> y=15-x (1)
5x+7y = 91 - (2)
put (1) into (2)
5x + 7(15-x) = 91
105 -2x = 91
2x = 17
x=7
therefore 7 pieces of cake are sold