NCHMCT JEE 2013 Question Paper with solutions for online practice

Question : 91 of 200

Marks: +1, -0

If a man can row 30 km down stream and 18 km upstream, each in three hrs, What is the speed of boat in still water?

Solution:

Let speed of boat = x km/hr
and speed of stream = y km/hr
Then,

{30}/{x+y}

= 3 and

{18}/{x-y}

= 3
⇒ 3x + 3y = 30 ...(i)
and 3x – 3y = 18 ...(ii)
Adding (i) and (ii), 6x = 48
∴ x = 8
Hence, speed of boat in still water = 8 km/hr.

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