Let the speed of boat in still water be x km/hr
Then, x + 1.5 = 15

Correct Option: C

Let the speed of boat in still water be x km/hr
Then, x + 1.5 = 15
⇒ x = 13.5

∴ Speed upstream = (13.5 - 1.5) km/hr = 12 km/hr

Speed of current = 5 - 3.5 = 1.5 km/hr.

Correct Option: B

Speed of current = 5 - 3.5 = 1.5 km/hr.
So the speed of man along the current = 5 + 1.5 = 6.5 km/hr

Let the rate against the current be x km/hr.
Then, (12 - x) / 2 = 1.5

Correct Option: A

Let the rate against the current be x km/hr.
Then, (12 - x) / 2 = 1.5
⇒ 12 - x = 3
⇒ x = 9 km/hr

Speed upstream = (40/8) km/hr = 5 km/hr
Speed downstream = (36/6) km/hr = 6 km/hr

Speed of boat in still water = (5 + 6)/2 km/hr = 5.5 km/hr.

Correct Option: C

Speed upstream = (40/8) km/hr = 5 km/hr
Speed downstream = (36/6) km/hr = 6 km/hr

Speed of boat in still water = (5 + 6)/2 km/hr = 5.5 km/hr.

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

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