Question
The speed of a boat in calm water is 4 km/hr greater
than the speed of the stream. The boat travels a distance of 280 km downstream and 200 km upstream in a total of 70 hours. What is the boat's speed while moving downstream?Solution
Let the speed of the boat in still water and speed of stream be 'x' km/hr and 'y' km/hr respectively. Given, (x - y) = 4 km/hr ATQ, {280 ÷ (x + y) } + {200 ÷ (x - y) } = 70 Or, {280 ÷ (x + y) } + {200/4} = 70 Or, {280 ÷ (x + y) } + 50 = 70 Or, {280 ÷ (x + y) } = 70 - 50 Or, {280 ÷ (x + y) } = 20 So, (x + y) = 14 Therefore, downstream speed of the boat = (x + y) = 14 km/hr
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