Question
The ratio of the speed of boat in upstream to speed of
boat in downstream is 7:9. If the boat can cover a total of 49 km upstream and 81 km downstream in 4 hours, then find the time taken by the boat to cover 128 km in still water.Solution
Let speed of boat in upstream and downstream be ‘7x’ km/h and ‘9x’ km/h respectively. 49/7x + 81/9x = 4 7/x + 9/x = 4 16 = 4x x = 4 Speed of boat in still water = (7x + 9x)/2 = 8x = 8 × 4 = 32 km/h Desired time = 128/32 = 4 hours
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