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Four friends A, B, C and D need to cross a bridge. A maximum of two persons can cross it at a time. It is night and they just have one lamp. Persons…

IAS 2016CSAT Reasoning

2016mcqmedium

Four friends A, B, C and D need to cross a bridge. A maximum of two persons can cross it at a time. It is night and they just have one lamp. Persons that cross the bridge must carry the lamp to find the way. A pair must walk together at the speed of slower person. After crossing the bridge, the person having faster speed in the pair will return with the lamp each time to accompany another person in the group. Finally, the lamp has to be returned at the original place and the person who returns the lamp has to cross the bridge again without lamp. To cross the bridge, the time taken by them is as follows:

A: 1 minute,
B: 2 minutes,
C: 7 minutes and
D: 10 minutes.

What is the total minimum time required by all the friends to cross the bridge?

Official previous-year question

Prelims CSAT (Paper II) · Held on 7 Aug 2016.

Options

  1. A23 minutes
  2. B22 minutes
  3. C21 minutes
  4. D20 minutes

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