A boat covers x + 20 km downstream or x - 5 km upstream in 5 hours. If the speed of the boat in still water is 300% more than the speed of the stream, find the value of x (in km).

42.5 km
40 km
45 km
37.5 km

Correct answer: 42.5 km

Solution

Downstream speed is \((x+20)/5\) and upstream speed is \((x-5)/5\). Let stream speed be s and boat speed in still water be b. Given b is 300% more than s, so b = 4s, and downstream/upstream speeds are b+s and b-s respectively.

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