A movie theater runs two films continuously. One film runs for 85 minutes and a second film runs for 100 minutes. Both movies begin at noon. When will the two films start again at the same time?

Answer 1

This is just like finding the LCM of 85 and 100
85 = 5x17
100 = 5x20
LCM = 5x17x20 = 1700

e.g.
85 170 255 ... 1615 1700 ...
100 200 300 .. 1600 1700 ..

It will take 1700 minutes = 28 hrs. 20 minutes.

Add that time to your noon.