You are frying fishes on a pan which can accommodate only 2 fishes at one time. It takes 5 minutes to fry one side of the fish.

What is the shortest time in which you can fry 3 fishes in the same pan ?

15 minutes.

Put 2 fishes in the pan. Fry for 5 minutes and then take out one and turn the other one. Also put in the third fish. Now fry for 5 minutes. The fish that you turned must be ready now so take it off while turning the other one. Also put in the fish which was fried from one side only in the pan. Fry them for 5 minutes and all the three fishes are fried now.