Question

the speed of boat in still water is 11km/hr .it can go 12km upstream & return downstream to the original point in 2hours 45minute.find the speed of the stream

Answer 1

Let the speed of the stream be 'x'km/hr.
The speed of boat in still water = 11km/hr
Therefore , the speed of boat in upstream = 11-x km/hr
And the speed of boat downstream = 11+x km/hr
A/Q,
12 /11 -x +12/11+x= 2 3/4 

⇒12 (1/ 11 -x+1/ 11 +x)= 11 / 4 

⇒ 22 / 121 - x2 = (11 / 4)×12
⇒ 22/ 121 - x2 = 11 / 48

 ⇒ 1331 -11 x2 = 1056 

⇒ 11 x2 = 275 
⇒ x2 = 25

Therefore , × = +5 or x = -5
As speed can't be negative ,so x is not equal to -5
Hence , The speed of the stream = 5km/hr.