The Torchlight
Riddle: Your name is A and you are with 3 of your friends - B, C, D. It's nighttime and you come through a forest. You all have only one torch and only 2 of you can use it at a time. The time taken by each person to cross the forest is - A = 1 min; B = 2 min; C = 7 min; D = 10 min; What is the least time taken for you all to cross the forest?
Answer: AB = 2 min (go to the end); A = 1 min (comes back); CD = 10 min (go to the end); B = 2 min (comes back, you came back alone in step 2); AB = 2 min (go to the end); Total = 17 mins.
Source: https://www.riddles.com/index.php/10901
