Question

A man can row 18kmph in still water. it takes him thrice as long as to row up as to row down the river. find the rate of stream (in kmph).

Answer 1

Rate of flow of the stream = r kmph
Rowing speed = 18 kmph
Distance traveled upstream or downstream = d km

Time to row upstream = d/(r-18) = 3* d/(r+18)

Solving, r = 38 kmph

Answer 2

Answer:

9 kmph(kilometer per hour)

Step-by-step explanation:

Let "x" be the rate of current.  

Then,  

Speed downstream  =  18 - x

Speed upstream  =  18 + x

Let us assume that the man travels 100 kms.  

Time downstream  =  100 / (18 + x) km/hr

Time upstream  =  100 / (18 - x) km/hr

Given : It takes him thrice as long as to row up as to row down the river.  

So, we have  

Time upstream  =  3 ⋅ Time downstream

• 100 / (18 - x)  =   3 ⋅ 100 / (18 + x)
• 1 / (18 - x)  =  3 / (18 + x)
• 1(18 + x)  =  3(18 - x)
• 18 + x  =  54 - 3x
• 4x  =  36
• x  =  9

So, the rate of current is 9 kmph.