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19
Q:

Rajesh rows in still water with a speed of 4.5 kmph to go to a certain place and comes back. Find his average speed for the whole journey, if the river is flowing with a speed of 1.5 kmph?

A) 2 kmph B) 4 kmph
C) 6 kmph D) 8 kmph

Answer:   B) 4 kmph



Explanation:

Let the distance in one direction = k kms

Speed in still water = 4.5 kmph

Speed of river = 1.5

Hence, speed in upstream = 4.5 - 1.5 = 3 kmph

Speed in downstream = 4.5 + 1.5 = 6 kmph

Time taken by Rajesh to row upwards = k/3 hrs

Time taken by Rajesh to row downwards = k/6 hrs

Now, required Average speed =Total distanceTotal speed = 2kk3 + k6 = 2k x 186k + 3k = 4 kmph 

 

Therefore, the average speed of the whole journey = 4kmph.

Subject: Boats and Streams
Exam Prep: AIEEE , Bank Exams , CAT , GATE , GRE
Job Role: Analyst , Bank Clerk , Bank PO , Database Administration
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The upstream speed of the boat is 40 kmph and the speed of the boat in still water is 55 kmph. What is the downstream speed of the boat?

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A man can row his boat at a speed of speed of 4 kmph and he finds that the time taken rowing upstream is double to that taken downstream. Find the speed of the stream (in kmph).

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