Alex ate 1/3 of a box of cookies. Then Beth ate 1/4 of what was left after Alex had finished. Finally, Carmine ate 1/5 of what was left after Beth had finished. When Carmine was done, only 36 cookies were left. How many cookies were in the box originally?

Answer 1

Alex ate 1/3, leaving 2/3
Beth ate 1/4 * 2/3 = 1/6, leaving 1/2
Carmine ate 1/5 * 1/2 = 1/10, leaving 2/5
so, 2/5 x = 36
x = 90