A person can swim in still water with a speed of 12 km/h. If the speed of the stream is 3 km/h, what will be the time taken by the person to go 54 km upstream?

Question: A person can swim in still water with a speed of 12 km/h. If the speed of the stream is 3 km/h, what will be the time taken by the person to go 54 km upstream?

Solution:
Given,
Speed of the person in still water = 12 km/h
Speed of the stream = 3 km/h
Distance to be covered upstream = 54 km
We know,
The effective speed = Speed in still water - Speed of stream
= (12 - 3) km/h
= 9 km/h

Time = (Distance ÷ Effective speed) hours
= (54 ÷ 9) hours
= 6 hours