Speed of a boat in still water is 10 km/h while the

Solution

For I: Speed of boat = 10 km/h Speed of stream = 3 km/h Speed in upstream = 10 – 3 = 7 km/h Speed in downstream = 10 + 3 = 13 km/h Total time = 100/7 + 150/13 = 14.29 + 11.54 = 25.83 hours So, I can’t be the answer. For II: Speed of boat = 10 km/h Speed of stream = 2 km/h Speed in upstream = 10 – 2 = 8 km/h Speed in downstream = 10 + 2 = 12 km/h Total time = 100/8 + 150/12 = 12.5 + 12.5 = 25 hours So, II can’t be the answer. For III: Speed of boat = 10 km/h Speed of stream = 4 km/h Speed in upstream = 10 – 4 = 6 km/h Speed in downstream = 10 + 4 = 14 km/h Total time = 100/6 + 150/14 = 16.67 + 10.71 = 27.38 hours So, III can’t be the answer. For IV: Speed of boat = 10 km/h Speed of stream = 5 km/h Speed in upstream = 10 – 5 = 5 km/h Speed in downstream = 10 + 5 = 15 km/h Total time = 100/5 + 150/15 = 20 + 10 = 30 hours So, IV can't be the answer.