Trains Boats and Streams Practice Test 1 with solutions

Question : 5 of 40

Marks: +1, -0

A motorboat, whose speed is 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. What is the speed of the stream (in km/hr)?

Validate

Solution:

Let speed of the stream be x km/hr, then

{30}/{15+x}+{30}/{15-x}

4 1/2

⇒

{30×30}/{225-x^2}

9/2

⇒

{200}/{255-x^2}

= 1
⇒

x^2

= 225 - 200
⇒

x^2

= 25
∴ x = 5 km/hr.

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