Manoj can row at the speed of 108 km/hr in still water and he rows the same distance in upstream and downstream which flows at a speed of 5 m/s. Find the average speed throughout the journey.?

Option 4 : 105 km/hr

GIVEN:

Speed of boat in still water(x) = 108 km/hr

Speed of stream(y) = 5 m/s = 18 km/hr

FORMULA USED:

When the distance is same then

Average speed = (2 × a × b)/(a + b)

Where a and b are two speed travelled

FORMULA USED:

Speed of a boat in still water be x km/hr and the speed of a stream be y km/hr.

Upstream speed = (x – y) km/hr

Downstream speed = (x + y) km/hr

CALCULATION:
Now,

Average speed = ((2 × (x + y)(x – y))/(x + y + x – y)

⇒ Average speed = 2 × /(2x)

⇒ Average speed = 2 × (108)² – (18)²)/ (2 × 108)

⇒ Average speed = (11664 – 324)/(108)

⇒ Average speed = 11340/108 = 105 km/hr

∴ Average speed = 105 km/hr