A boat takes 45 minutes less to travel 18 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 5 kmph, the speed of the stream is :

2 kmph

3 kmph

1 kmph

1.5 kmph

Let the speed of the stream be x mph. then, Speed downstream = (5+x) mph, speed upstream = (5-x) mph. .'. 18/(5-x) + 18/(5+x) = 45/60 => 18(5+x -5+x) = 45/60 (25 - x^2) => 24x = 25 -x^2 => x^2+24x -25 =0 => (x-1)(x+25) = 0 => x = 1 mph.

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