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 ofA: 1 minute to cross bridgeB: 2 minutes to cross bridgeC: 8 minutes to cross bridgeD: 11 minutes to cross bridgeNow question is… "what is the total minimum time required by all 4 friends to cross the bridge….?
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Answer:
A+B =2 minutes
A returns=1 minute
A+C=7 minutes
A+D=10 minutes
A comes back =1 minute Leaves lamp and crosses again=1 minute
Total 23 minutes.
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