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  1. The speed of a boat in still water is 10 km/h. If it can travel 26 km downstream and 14 km upstream in the same time , then the speed of stream is ?
    1. 2 km/h
    2. 2.5 km/h
    3. 3 km/h
    4. None of these
Correct Option: C

Let the speed of the stream = x km/h
∴Speed of boat in still water = 10 km/h
Speed of boat downstream = ( x + 10) km/h
Speed of boat upstream=(10 - x) km/h

∴ Time taken to travel 26 km downstream=[ 26 / ( 10 + x ) ] h
Time taken to travel 14 km upstream=[ 14 /( 10 - x )] h
⇒ By condition [ 26 / ( 10 + x)]=[ 14 / ( 10 - x)]
⇒ 26(10-x)=14(10+x)

⇒ 260-26x =140 + 14x
⇒ 40x=120
⇒ x = 3 Here, speed of stream = 3 km/h


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