Speed of a boat in still water is 10 km/h while the speed of stream is ____ km/h. Total time taken by the boat to go 100 km upstream and 150 km downstream is ____ hours. The values given in which of the following options will fill the blanks in the same order in which it is given to make the above statement true:

I. 3, 20

II. 2, 18

III. 4, 19

IV. 5, 22

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 be the answer.