Correct Answer - Option 2 : 2.4 hours
Given:
Speed of boat in downstream = 12 km/hr
Speed of boat in upstream = 8 km/hr
Total distance = 24 km
Concept used:
Speed of boat in upstream = u – v
Speed of boat in downstream = u + v
Where,
u = speed of boat in stationary water
v = speed of river
Formula used:
Speed = Distance/Time
Calculations:
u + v = 12 ----(i)
u - v = 8 ----(ii)
On adding equation (i) and (ii),
(u + v) + (u - v) = 12 + 8
⇒ 2u = 20
⇒ u = 10 km/hr
Time = Distance/speed
⇒ 24/10
⇒ 2.4 hours
∴ It will take 2.4 hours to cover a distance of 24 km in stationary water.