Question

A cook wants to prepare some food to be cooked by 1:15 p.m. He uses an oven with an automatic timer that can switch on and off at a certain times. The oven needs to be on for 2 hours 10 minutes. At which time does the oven needs to switch on?

Answer 1

$$t=13\ h\ 15\ min-2\ h\ 10\ min=11\ h\ 05\ min\\t=11\ h\ 05\ min\ a.m.$$