A boat covers a distance of 40 km in downstream, then it increases its speed by 2 km/hr and covers a distance of 36 km then again speed is increased by 3 km/hr and covers a distance of 45 km. If the speed of the boat in still water is 8 km/hr and speed of stream is 2 km/hr. Find the average speed of the boat.

A boat covers a distance of 40 km in downstream, then it increases its speed by 2 km/hr and covers a distance of 36 km then again speed is increased by 3 km/hr and covers a distance of 45 km. If the speed of the boat in still water is 8 km/hr and speed of stream is 2 km/hr. Find the average speed of the boat.

1). 12.5 km/hr
2). 12.1 km/hr
3). 12.4 km/hr
4). 12.8 km/hr

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Guest · Answer 1 · 2019-07-07 13:31:22

Let speed of boat in still water is S_B, speed of stream is SC, and Speed of boat in downstream is S_D

Speed of boat in downstream, S_D = S_B + S_C = 8 + 2 = 10 km/hr

Average Speed of the boat $(= \frac{{40\; + \;36\; + \;45}}{{\frac{{40}}{{10}}\; + \;\frac{{36}}{{10\; + \;2}}\; + \;\frac{{45}}{{12\; + \;3}}}} = \frac{{121}}{{4\; + \;3\; + \;3}} = \frac{{121}}{{10}})$

∴ Average Speed of the boat = 12.1 km/hr

Guest · Answer 2 · 2019-07-07 13:31:24

Let speed of boat in still water is S_B, speed of stream is SC, and Speed of boat in downstream is S_D

Speed of boat in downstream, S_D = S_B + S_C = 8 + 2 = 10 km/hr

Average Speed of the boat $(= \frac{{40\; + \;36\; + \;45}}{{\frac{{40}}{{10}}\; + \;\frac{{36}}{{10\; + \;2}}\; + \;\frac{{45}}{{12\; + \;3}}}} = \frac{{121}}{{4\; + \;3\; + \;3}} = \frac{{121}}{{10}})$

∴ Average Speed of the boat = 12.1 km/hr

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