Four friends Crossing a Bridge Puzzle

Q.

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

10 thoughts on “Four friends Crossing a Bridge Puzzle”

1. soumya says:

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?

Sorry, its wrong answer ! Its much lower 🙂

Sorry, its wrong answer ! Its much lower :). How about A and B go together?

1. soumya says:

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.

Hint , A and B go together first

Hey Soumya, We have updated the answer now. You were close 🙂

Please like us for more puzzles!

1. soumya says:

My answer was not close! 🙂 But yeah..good solution. I like your puzzles 🙂