Question

Vijay rows 3 km per hour in still water. if the river is running at 1 km per hour , it takes him 45 minutes to row to a place and back .how far is the place ?

Answer 1

3km/hr = in still water

river speed =1 km/h
speed=3km/h
time= 45min= 45/60=3/4hr
distance=speed/time taken

3/3/4=3/2 because its twice =distance is 1.5 km

Answer 2

Given:

• Speed of boat in still water = 3 Km/hr
• Speed of water = 1 Km/hr
• Time = 45 mins = 45/60 = 0.75 hrs

To Find:

• Distance of the place.

Solution:

• Speed of boat(upstream) = speed of boat in still water-speed of water = 3-1 = 2 Km/hr = $S_1$
• Speed of boat(downstream) = speed of boat in still water+speed of boat = 3+1 = 4 Km/hr = $S_2$
• WKT,
• $Time = \frac{Distance}{speed}$
• Here, we have two speeds, one for upstream and the other for downstream, hence we need to add them to get the final answer.
• Equation becomes, $T = \frac{D}{S_1}+\frac{D}{S_2}$
• $0.75 = \frac{D}{2}+\frac{D}{4}= \frac{3D}{4}$
• 3 = 3D
• D = 3/3 = 1Km

The place is 1 Km far.