Friday, August 30, 2013

Bridge Crossing - Different Speed - 1/2/7

There are Four persons. They need to cross a rickety bridge at night.

They have only one torch and the bridge is too dangerous to cross without one. The bridge is only strong enough to support two people at a time. Not all people take the same time to cross the bridge.

Each person takes different time to cross bridge. Times for each person are  1 min, 2 mins, 7 mins and 10 mins.

What is the shortest time needed for all four of them to cross the bridge?


  1. 21mins..
    First 1min and 10mins will go ( taking 10mins) ,then 1min will come back with torch (taking 1min). Then 1min and 7mins will go (taking 7mins) and 1min will come back again with torch (taking 1min). Then 1min and 2mins will go in 2mins.
    So total time : 10+1+7+1+2 = 21mins