how they will cross the bridge?

It is a very dark night. Allan, Brian, Chip and David want to cross the little narrow bridge from the west end to the east end with one flash light.

They need to finish it no more than 17 minutes.
Only 2 persons can be on the bridge at one time.
They always need a person to carry the flash light back to the west end for the next group to use.

Allan needs 10 minutes to cross the bridge.
Brian needs 5 minutes.
Chip needs 2 minutes.
David needs 1 minute.

If there are 2 persons on the bridge, they need to go by the speed of the slower pace person. How are you going to proceed?

Chip and David cross (2 minutes)
Chip comes back (2 minutes)
Allan and Brian cross ( 10 minutes)
David comes back ( 1 minute)
Chip and David cross ( 2 minutes)

total = 17 minutes

[QUOTE=jainbrijesh;11791]It is a very dark night. Allan, Brian, Chip and David want to cross the little narrow bridge from the west end to the east end with one flash light.

They need to finish it no more than 17 minutes.
Only 2 persons can be on the bridge at one time.
They always need a person to carry the flash light back to the west end for the next group to use.

Allan needs 10 minutes to cross the bridge.
Brian needs 5 minutes.
Chip needs 2 minutes.
David needs 1 minute.

If there are 2 persons on the bridge, they need to go by the speed of the slower pace person. How are you going to proceed?[/QUOTE]

Ans) Phases time taken at east end
first: C+D 2 min -
returns: D 1 min C
second: A+B 10 min C
Returns: C 2 min A, B
Third: C+D 2 min A, B, C, D
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Total 17 min
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here A,B,C,D stands for initials of their names.