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How can all four men cross the bridge in 17 minutes?

+2 votes
252 views

Four men want to cross a bridge. They all begin on the same side. It is night and they have only one flashlight with them. At most two men can cross the bridge at a time and any party who crosses, either one or two people, must have the flashlight with them. The flashlight must be walked back and forth: it cannot be thrown, etc. Each man walks at a different speed. A pair must walk together at the speed of the slower man. Man 1 needs 1 minute to cross the bridge, man 2 needs 2 minutes, man 3 needs 5 minutes, and man 4 needs 10 minutes. For example, if man 1 and man 3 walk across together, they need 5 minutes.

How can all four men cross the bridge in 17 minutes?

posted May 8, 2014 by Madhavi Latha

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3 Solutions

+2 votes

First Man 1 & Man 2 will cross so 2mints
then Man 1 returns so 1mint
then Man 10 & Man 5 will cross so 10mints
then Man 2 returns so 2mints
finally Man 1 & Man 2 will cross so 2mints

Thus total time taken ( 2+1+10+2+2)17mints

solution May 12, 2014 by Kunal Shah
+1 vote

MAN 1 AND MAN2 CROSS =2MIN
MAN 1 RETURN=1MIN
MAN 3 AND MAN 4 CROSS =10MIN
MAN 2 RETURN=2MIN
MAN1 AND MAN2 CROSS=2MIN

solution Jun 23, 2014 by anonymous
+1 vote

A and B cross first using up 2 minutes.
A comes back making it 3
C and D cross making it 13 minutes
then B crosses back over making it 15 minutes.
And finally A and B cross together to make it 17 minutes.

solution Jul 7, 2015 by Vrije Mani Upadhyay



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0 votes

A group of four people wants to cross bridge. It is dark, and they have to light the path with a torch. No more than two people can cross the bridge simultaneously, and the group has only one torchlight. It takes different time for the people in the group to cross the bridge:

A crosses the bridge in 1 minute,
B crosses the bridge in 2 minutes,
C crosses the bridge in 5 minutes,
D crosses the bridge in 10 minutes.

How can the group cross the bridge in 17 minutes?

0 votes

Four jolly men sat down to play, they played all night until the break of day.
They played for cash and not for fun, with a separate score for every one.
When it came time to square accounts, they all made quite fair amounts.
Not one lost and all gained.
Now that you've heard, can you explain?

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