A boat takes 2 hours more to travel 45 km upstream than to travel the same distance downstream. If the ratio of the speed of the current to the speed of the boat is 1:4, then find the speed of the current.

5 km/hr
9 km/hr
3 km/hr
6 km/hr

Correct answer: 3 km/hr

Solution

If the speed of the boat in still water is 4x and the speed of the current is x, then upstream speed = 3x and downstream speed = 5x. For 45 km, the time difference is \(45/3x - 45/5x = 2\), which gives x = 3.

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