Four friends Crossing a Bridge Puzzle

Q.

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Quiz time:-
A very interesting puzzle.

Lets see who solves this.
Four friends A, B, C, D
Need to cross a bridge..
A maximum of 2 peoples can cross at a time..
It is night and they have just 1 lamp.
People that cross the bridge must carry the lamp to see the way..
A pair must walk together at the speed of slower person…

Speeds of
A: 1 minute to cross bridge
B: 2 minutes to cross bridge
C: 9 minutes to cross bridge
D: 10 minutes to cross bridge


Now question is…
“what is the total minimum time required by all 4 friends to cross the bridge….?”

Ans is:

A+B cross with lamp => 2 min
A comes back with lamp => 1 min

C+D cross with lamp =>10 min
B comes back with lamp => 2 min
A+B cross with lamp => 2 min

Total 2+1+10+2+2 = 17 min

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10 thoughts on “Four friends Crossing a Bridge Puzzle

  1. A+D cross with lamp => 10 min
    A comes back with lamp => 1 min
    A+C cross with lamp =>9 min
    A comes back with lamp => 1 min
    A+B cross with lamp => 2 min

    Total 10+1+9+1+2 = 23 min

    Is it correct?

      1. They do go together once. Considering the conditions mentioned – “People that cross the bridge must carry the lamp to see the way. And a pair must walk together at the speed of slower person”, I think the fastest person should be the one to do all the running with the lamp. So A will accompany 2 of the others and come back with lamp and cross the bridge with the last person.

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