Four friends A, B, C, D

Need to cross a bridge..

A maximum of 2 people 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: 5 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….?

See Solution : BridgePerson A : 1 minute

Person B : 2 minutes

Person C : 5 minutes

Person D : 10 minutes

Person C and D are the slowest guys, if they don’t walk together that it self will make it 15 minutes, In this case (the best way to save time is) :

Initially A,B,C,D ========

First A& B will cross the bridge and A will come back => time taken 2 + 1 => 3

A,C,D ======== B

Now C & D should cross the bridge together and B will come back => time taken 10 + 2 => 12

Now A & B will cross the bridge together => time taken 2

total time 3 + 12 + 2 => 17

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