Boats and Streams Practice Questions

5 questions per page • Detailed step-by-step solutions

Question 21
Easy
Two boats A and B start towards each other from two places, 150 km apart. Speed of the boat A and B in still water are 16 km/hr and 14 km/hr respectively. If A proceeds down and B up the stream, they will meet after.
A 4.5 hours
B 4 hours
C 5 hours
D 6 hours
Correct Answer: C

Explanation:

Distance = 150 km. Speed of A downstream = 16 + v, speed of B upstream = 14 - v. Relative speed of approach = (16 + v) + (14 - v) = 30 km/hr. Time to meet = 150 / 30 = 5 hours.
Question 22
Easy
A man swims downstream distance of 15 km in 1 hour. If the speed of the current is 5 km/ hr, the time taken by the man to swim the same distance upstream is :
A 1 hr 30 min
B 45 min
C 2 hr 30 min
D 3 hrs
Correct Answer: D

Explanation:

Downstream speed = 15 / 1 = 15 km/hr, current = 5 km/hr => still water = 10 km/hr. Upstream speed = 10 - 5 = 5 km/hr. Time upstream = 15 / 5 = 3 hours.
Question 23
Easy
Two boats A and B are sailing in two different rivers namely P and Q. Ratio of upstream speeds of boat A to B in their respective river is 1:1. Find the ratio of difference between the still water speeds of boats A and B to the difference of stream speeds of rivers P and Q.
A 1 : 1
B 1 : 2
C 2 : 1
D 2 : 3
Correct Answer: A

Explanation:

Upstream speed of A = uA - vP, Upstream speed of B = uB - vQ. Ratio is 1 : 1 => uA - vP = uB - vQ => uA - uB = vP - vQ => (uA - uB) / (vP - vQ) = 1 : 1.
Question 24
Medium
A boat can travel 10 km in 12 minutes when the water is still. If the ratio between the speeds of the boat in still water and the speed of the current is 5 : 1, then find the time taken by the boat to travel 80 km against the stream.
A 3.5 hours
B 2.75 hours
C 2 hours
D 1.25 hours
Correct Answer: C

Explanation:

Boat speed in still water = 10 / (12/60) = 50 km/hr. Ratio boat : stream = 5 : 1 => stream = 10 km/hr. Upstream speed = 50 - 10 = 40 km/hr. Time for 80 km upstream = 80 / 40 = 2 hours.
Question 25
Easy
A boat can cover 720 km distance downstream in 40 hours. The speed of boat in still water is double the speed of the stream. Then find out the time taken by boat to cover 480 km distance in upstream.
A 100 hours
B 60 hours
C 40 hours
D 80 hours
Correct Answer: D

Explanation:

Downstream speed = 720 / 40 = 18 km/h. Given u = 2v => 3v = 18 => v = 6 km/h, u = 12 km/h. Upstream speed = 12 - 6 = 6 km/h. Time upstream = 480 / 6 = 80 hours.