How many cakes and cream puffs were in the shop at first?

Question

In a pastry shop, the number of cakes was twice the number of cream puffs. After 90 cakes and 42 cream puffs were sold, the ratio of the number of cakes left to the number of cream puffs left was 2 : 5. How many cakes and cream puffs were in the shop at first?

Answer 1

start: x=2y or y=x/2... later: 2(x-90)=5*(y-42)... 2x-180=5y-210... 2x-5y=180-210=-30... 4y-5y=-30... y=30, so x=60