Download Boat and Streams Questions and Answers PDF for SBI, IBPS, CET, RRB and Clerk 2020

Direction : Read the following questions carefully and choose the right answer.
1
Ratio between speed of boat in still water to speed of stream is 5 : 2. If 224 km is travelled by downstream in 4 hours then find the difference between speed of boat in still water and speed of stream?
» Explain it
A
Let the speed of boat in still water and speed of stream be 5x and 2x respectively.

According to the question,

224  = 5x + 2x
4

x =  224  × 4
7

x =  32  = 8
4

Required difference = 5x – 2x = 3x

3x = 24 km/hr

Hence, option A is correct.
2
If the upstream speed of a boat is 50% less than the downstream speed of the boat and if a object is thrown in the river it covers 100m in 50 sec, then how much distance boat can cover in still water in 5 hours?
» Explain it
D
Let the speed of boat in still water be s m/sec

As the object covers 100m in 50 sec , so the distance travelled by the object will be with the help of the speed of the stream only.

Speed of stream =  100  = 2 m/s
50

Given that,

(s – 2) = (s + 2) – 50 (s + 2)/100

(s – 2) = (s + 2)(1 – 1/2)

s = 6 m/sec

s =  6 × 18  =  108  km/hr
5 5

Distance covered by the boat in still water in 5 hours

= 108 ×  5  = 108 km
5

Hence, option D is correct.
3
A steamer can go 12 km in still water in 25 minutes. One day, it went 11.25 km upstream and returned the same distance in downstream. If the difference between the time taken to travel upstream and downstream was 12.5 minutes, then what was the speed of stream in km per hour?
» Explain it
A
In still water, the speed of steamer =  12000
25

= 480 meter per minute = 8 meters per second

Let the speed of stream = v m/sec

In upstream, the speed of steamer = (8 – v) m/sec

In downstream, the speed of steamer = (8 + v) m/sec

According to the question,

11250  –  11250  = 12.5 × 60 = 750 seconds
8 – v 8 + v

By solving, v = 2 meters per second

2 × 18  = 7.2 km per hour
5

Hence, option A is correct.
4
The ratio of speed of A and B in still water is 3 : 2. A and B start from the same point in the river, A goes upstream and B goes downstream. After 3 hours the stream stops flowing and A starts rowing in the opposite direction to meet B. How much time after the stream stops flowing does A meet B?
» Explain it
B


Let the speed of current be = c km/hr
 
Let the speeds of A and B in still water be 3k km/hr and 2k  km/hr
 
Upstream speed of A = (3k – c) km/hr
 
Downstream speed of B = (2k + c) km/hr
 
Distance between A and B after 3 hrs = [3 (3k – c) + 3 (2k + c)] km
 
= (9k – 3c + 6k + 3c) km 
 
= 15k km
 
After stream becomes stationary
 
Relative speed when both go in same direction = (3k – 2k) km/hr = k km/hr
 
Time after which they meet = 15 k/ k = 15 hrs
 
Hence, option B is correct.
5
A boat goes a certain distance upstream and comes back downstream to the starting point in 144 min. If the speed of the boat in still water becomes 66.67% of the original, time taken for the same journey will be 224 min. What is the ratio of the speed of boat in still water and speed of current?
» Explain it
B
Let the distance be D and Speed of boat in still water be 3B and that of current be C

D  +  D  = 144 ..........eq.(i)
3B + C 3B – C

When the speed of the boat becomes 66.67% → new boat speed = 2B

D  +  D  = 224 ..........eq.(ii)
2B + C 2B – C

Dividing eq. (i) by eq. (ii)

6B  =   
(3B + C) (3B – C) 144
4B 224
(2B + C) (2B – C)  

6 × (4B2 – C2)  =  9
4 × (9B2 – C2) 14

4B2 – C2  =  3
9B2 – C2 7

B2 = 4C2 →  B  =  2
C 1

3B  =  6
C 1

The ratio of speed of boat and current in 6 : 1

Hence, option B is correct.