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    Question

    A man goes downstream with a boat to some destination

    and returns upstream to his original place in 5 hours. If the speed of the boat in still water and the stream are 10km/h and 4km/h respectively, the distance of the destination from the starting place is. 
    A 24km Correct Answer Incorrect Answer
    B 21km Correct Answer Incorrect Answer
    C 12km Correct Answer Incorrect Answer
    D 14km Correct Answer Incorrect Answer

    Solution

    Let the speed of boat in still water =B and speed of stream =S then Given – B=10km/h, S=4km/h Speed of boat in downstream =B+S=10+4=14 B+S=14           … (1) Speed of boat in upstream =B-S=10-4=6 B-S=6  … (2) Average speed = (14×6)/14+6 =84/20=4.2km/h now the distance of the destination from the starting place is.  =5×4.2 =21km.

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