Question

The speed of the boat in still water is 11 km. it can go to 12 km upstream nd return downstream in 2 hrs 45 min find the speed of the boat

Answer 1

here is the answer

Let the speed of the stream be "x km/ hr.n

. Speed of boat in still water = 11 km/ hr.

 Therefore, speed of boat upstream = 11 - x 

speed of boat downstream = 11 + x

 A.T.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

⇒ x = + 5 or - 5 

As speed can't be negative, x not equal to -5. 

Therefore Speed of stream = x = 5 km / hr.