Question
Speed of a boat in still water is 3 times more than the
speed of stream. If boat covers 135 km in downstream in 9 hours, then find the time taken by the boat to cover 108 km in upstream.Solution
Let the speed of stream be ‘x’ km/hr. So, speed of boat in still water = 4 × x = 4x km/hr Downstream speed of boat = 4x + x = 5x km/hr According to question; 5x = 135/9 = 15 Or, x = 3 Upstream speed of the boat = 4x – x = 3x = 3 × 3 = 9 km/hr Required time taken = 108/9 = 12 hours
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