Question
A Boat travel 80 km distance in downstream and 48 km
upstream and the total time taken is 20 hours. The same boat travels 30 km distance in downstream as much time travel 12 km in upstream. Find the speed of boat in still water?Solution
Let the speed of stream be x And speed of Boat be y Total time taken =80/(x+y) + 48/(x - y) = 20 ………………………. (i) And time taken for 30 km in downstream and 12 km in upstream is equal 30/(x + y) = 12/(x - y) 5x – 5y = 2x + 2y 3x = 7y x/y = 7/3 Now x = 7k and y = 3k Put the value of x and y in equation (i), 80/(7k + 3k) + 48/(7k - 3k) = 20 80/10k + 48/4k = 20 8/k + 12/k = 20 20/k = 20 k = 1 Therefore the speed of Boat in still water is 7 × 1 = 7 km/hr
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