Four People need to cross a rickety bridge at night. Unfortunately they have only one torch and the bridge is too dangerous to cross with out one. The bridge is strong enough to support two people at a time and torch is required to cross bridge. Not all the people take the same time to cross the bridge. Times for each person:: 1 mins, 2 mins, 7 mins, 10 mins. What is the shortest time needed for all four of them to cross the bridge??
We have to see that who goes slow go together and do not come back.
1 and 2 cross the bridge : 2 min
1 comes back with torch : 1 min
7 and 10 cross the bridge : 10 min
2 comes back with torch : 2 min
1 and 2 cross the bridge : 2 min
Total time = 2 + 1 + 10 + 2 + 2 = 17 mins
1 and 2 cross the bridge : 2 min
1 comes back with torch : 1 min
7 and 10 cross the bridge : 10 min
2 comes back with torch : 2 min
1 and 2 cross the bridge : 2 min
Total time = 2 + 1 + 10 + 2 + 2 = 17 mins
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