New Student Offer - HELLO

# Boats and Streams Important Questions with Explanations

### Ques 1.

A man can swim downstream at 8 km/h and upstream at 2 km/h. Find man's rate in still water and the speed of the current.
a) 5 km/h and 3 km/h respectively
b) 7 km/h and 5 km/h respectively
c) 2 km/h and 9 km/h respectively
d) 8 km/h and 10 km/h respectively
e) None of The Above

### Ques 2.

A man takes 3 hours 45 minutes to row a boat 15 km downstream of a river and 2 hours 30 minutes to cover a distance of 5 km upstream. Find the speed of the river current in km/hr.
a) 1 km/hr
b) 3km/hr
c) 5 km/hr
d) 9 km/hr
e) None of The Above

### Ques 3.

A man can row upstream at 7 km/h and downstream at 10 km/h. Find man's rate in still water and the rate of current.
a) 6 km/h and 3.4 km/h respectively
b) 9 km/h and 2.5 km/h respectively
c) 8.5 km/h and 1.5 km/h respectively
d) 10 km/h and 2.3 km/h respectively
e) None of The Above

### Ques 4.

A man can row 7 (1/2) km/h in still water. If in a river running at 1.5 km an hour it takes him 50 minutes to row to a place and back, how far off is the place?
a) 8 km
b) 5 km
c) 3 km
d) 10 km
e) None of The Above

### Ques 5.

At his usual rowing rate, Rahul can travel 12 miles downstream in a certain river in 6 hours less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his 24 mile round trip, the downstream 12 miles would then take only one hour less than the upstream 12 miles. What is the speed of the current in miles per hour?
a) 1 (1/3)
b) 1 (2/3)
c) 2 (1/3)
d) 2 (2/3)
e) None of The Above

Q6. Amrit rows to a place 48 km distant and back in 14 hours. He finds that he can row 4km with the stream in the same time as 3 km against the stream. The rate of the stream is:
a) 1 km/h
b) 1.5 km/h
c) 1.8 km/h
d) 3.5 km/h
e) None of The Above

### Ques 7.

Prithviraj takes twice as long to row a distance against the stream as to row the same distance in favor of the stream. The ratio of the speed of the boat (in still water) and the stream is:
a) 2 : 1
b) 3 : 1
c) 3 : 2
d) 4 : 3
e) None of The Above

### Ques 8.

Akshay's speed with the current is 15 km per hour and the speed of the current is 2.5 km per hour. The man's speed against the current is:
a) 8.5 km per hour
b) 9 km per hour
c) 10 km per hour
d) 12.5 km per hour
e) None of The Above

### Ques 9.

If a boat goes 7 km upstream in 42 minutes and the speed of the stream is 3 km per hour, then the speed of the boat in still water is:
a) 4.2 km per hour
b) 9 km per hour
c) 13 km per hour
d) 21 km per hour
e) None of The Above

### Ques 10.

A motorboat, whose speed is 15 km per hour in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km per hour) is:
a) 4
b) 5
c) 6
d) 10
e) None of The Above

Watch Boats and Streams Video Lecture with Practice Questions here

### Solution

Man's rate in still water = 1/2 (Downstream Rate + Upstream Rate)
= 1/2 (8 + 2) = 5 km/h
Speed of Current = 1/2 (Downstream - Upstream Rate)
= 1/2 (8 - 2) = 3 km/h

Rate in still water = 1/2 (10 +7) km/h = 8.5 km/h
Rate of Current = 1/2 (10 - 7) km/h = 1.5 km/h

Speed Downstream = (7.5 + 1.5) kmph = 9 kmph
Speed Upstream = (7.5 - 1.5) kmph = 6 kmph
Let the required distance be x km. Then,
x/9 + x/6 = 50/60
2x + 3x = 5/6 × 18 = 5x = 15, x = 3
Hence the required distance is 3 km.

Akshay's rate in still water = (15 - 2.5) km per hour = 12.5 km per hour
Akshay's rate against the current = (12.5 - 2.5) km per hour = 10 km per hour

Rate upstream = (7/42 × 60) km per hour = 10 km per hour
Speed of stream = 3 km per hour
Let speed in still water be x km per hour. Then, speed upstream = (x - 3) km per hour
x - 3 = 10 or x = 13 km per hour