4 friends A B C D are trying to cross a forest. It takes 2,3,5,7 mins for each of them respectively. But they have only one torch and nothing else. And the condition is that the forest can be crossed only with torch and a maximum of two people can pass by the forest at a time. What will be the minimum time in which the forest can be crossed. (Hint: if A and B go together in a turn then they would take 3 mins as B takes 3).
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Here A takes 2 mins , B takes 3 mins , C takes 5 mins and D takes 7 mins to cross the forest.The minimum time in which the forest can be crossed :
1.AB cross - 3 mins
2.A comes back - 2 mins
3.CD cross - 7 mins
4.B comes back - 3 mins
5.AB cross - 3 mins
Therefore the minimum time taken = 3+2+7+3+3 = 18 mins