A man can row 10.2 km downstream in 18 minutes. If the speed of the stream is 3.5 km/h, how much time he would take to cover 121.5 km upstream? (in hours)
Let the speed of boat rowed by man by x.
A man can row 10.2 km downstream in 18 minutes i.e speed (x+3.5) = (10.2*60)/18
Hence, speed of boat = 30.5 km/hr
Now, relative speed of boat going downwards = 30.5-3.5 = 27km/hr
Now, number of hours required to row upwards = 121.5/27 = 4.5 hours = 4$$\frac{1}{2}$$
Option A is correct.
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