A boat goes 30 km upstream in 3 hours and downstream in 1 hour. How much time (in hours) will this boat take to cover 60 km in still water?
Answer & explanation
Correct answer: option 2
If we let the speed of the boat = a and the speed of the stream = b then,
Downstream = a + b
Upstream = a – b
According to the question
A boat goes 30 km upstream in 3 hours
= (a – b) = \(\frac{30}{3}\)
= a – b = 10 .....(1)
Again,
A boat goes 30 km downstream in 1 hour
= a + b = 30 .....(2)
Adding the equation (1) and (2), we get
= a – b = 10 + a + b = 30
= 2a = 40
= a = 20
Now,
Time taken to cover 60 km in still water \(\frac{60}{20}\) = 3