SBI Clerk 2018: Quantitative Aptitude Quiz for Prelims – 16

Hello and welcome to exampundit. Here is a set of Quantitative Aptitude Quiz on Boats & Streams for Prelims exam of SBI Clerk 2018.

 

  1. The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is

(a) 1.6 km

(b) 2 km

(c) 3.6 km

(d) 4 km

Answer & Solutions

Option: C

Explanation:

Speed downstreams =(15 + 3)kmph

= 18 kmph.

Distance travelled = (18 x 12/60)km

= 3.6km

 

 

 

  1. Sahil can row 3 km against the stream in 20 minutes and he can return in 18 minutes. What is rate of current ?

(a) 1/2 km/hr

(b) 1/3 km/hr

(c) 2 km/hr

(d) 4 km/hr

Answer & Solutions

Option: A

Explanation: Speed Upstream=3/20/60=9km/hrSpeed Downstream=3/18/60=10km/hrRate of current will be(10−9)/2=1/2km/hr

 

 

  1. A man can row at 5 kmph in still water. If the velocity of the current is 1 kmph and it takes him 1 hour to row to a place and come back. how far is that place.

(a) 4 km

(b) 1.4 km

(c) 2.4 km

(d) 3.4 km

Answer & Solutions

Option: C

Explanation:

Let the distance is x km

Rate downstream = 5 + 1 = 6 kmph

Rate upstream = 5 – 1 = 4 kmph

then

x/6 + x/4 = 1 [because distance/speed = time]

=> 2x + 3x = 12

=> x = 12/5 = 2.4 km

 

 

 

4 A boat can travel with a speed of 16 km/hr in still water. If the rate of stream is 5 km/hr, then find the time taken by the boat to cover distance of 84 km downstream.

(a) 4 hours

(b) 5 hours

(c) 6 hours

(d) 7 hours

Answer & Solutions

Option: A

Explanation:

It is very important to check, if the boat speed given is in still water or with water or against water. Because if we neglect it we will not reach on right answer. I just mentioned here because mostly mistakes in this chapter are of this kind only.

 

Lets see the question now.

Speed downstream = (16 + 5) = 21 kmph

 

Time = distance/speed = 84/21 = 4 hours

 

 

 

5 A man’s speed with the current is 20 kmph and speed of the current is 3 kmph. The Man’s speed against the current will be

 

(a) 11 kmph

(b) 12 kmph

(c) 14 kmph

(d) 17 kmph

Answer & Solutions

Option: C

Explanation:

If you solved this question yourself, then trust me you have a all very clear with the basics of this chapter.

 

If not then lets solve this together.

 

Speed with current is 20,

speed of the man + It is speed of the current

Speed in still water = 20 – 3 = 17

 

Now speed against the current will be

speed of the man – speed of the current

= 17 – 3 = 14 kmph

 

 

 

 

  1. A motorboat, whose speed in 15 km/hr 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/hr) is

(a) 2 km/hr

(b) 3 km/hr

(c) 4 km/hr

(d) 5 km/hr

Answer & Solutions

Option: D

Explanation:

Let the speed of the stream be x km/hr. Then,

Speed downstream = (15 + x) km/hr,

Speed upstream = (15 – x) km/hr

 

So we know from question that it took 4(1/2)hrs to travel back to same point.

 

So,

3015+x−3015−x=412=>900225−x2=92=>9×2=225=>x=5km/hr

 

 

 

  1. A man rows 750 m in 675 seconds against the stream and returns in 7 and half minutes. His rowing speed in still water is

(a) 4 kmph

(b) 5 kmph

(c) 6 kmph

(d) 7 kmph

Answer & Solutions

Option: B

Explanation:

Rate upstream = (750/675) = 10/9 m/sec

Rate downstream (750/450) m/sec = 5/3 m/sec

Rate in still water = (1/2)*[(10/9) + (5/3)] m/sec.

= 25/18 m/sec

= (25/18)*(18/5) kmph

= 5 kmph

 

 

 

 

  1. A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat in still water and stream is

(a) 3:1

(b) 1:3

(c) 2:4

(d) 4:2

Answer & Solutions

Option: A

Explanation:

Let speed downstream = x kmph

Then Speed upstream = 2x kmph

 

So ratio will be,

(2x+x)/2 : (2x-x)/2

=> 3x/2 : x/2 => 3:1

 

 

 

  1. If Rahul rows 15 km upstream in 3 hours and 21 km downstream in 3 hours, then the speed of the stream is

(a) 5 km/hr

(b) 4 km/hr

(c) 2 km/hr

(d) 1 km/hr

Answer & Solutions

Option: D

Explanation:

Rate upstream = (15/3) kmph

Rate downstream (21/3) kmph = 7 kmph.

Speed of stream (1/2)(7 – 5)kmph = 1 kmph

 

 

 

  1. A man can row 28/3 kmph in still water and finds that it takes him thrice as much time to row up than as to row, down the same distance in the river. The speed of the current is.

(a) 11/3 kmph

(b) 14/3 kmph

(c) 17/3 kmph

(d) 20/3 kmph

Answer & Solutions

Option: B

Explanation:

Friends first we should analyse quickly that what we need to calculate and what values we require to get it.

 

So here we need to get speed of current, for that we will need speed downstream and speed upstream, because we know

Speed of current = 1/2(a-b) [important]

 

Let the speed upstream = x kmph

Then speed downstream is = 3x kmph [as per question]

 

speed in still water = 1/2(a+b)=>1/2(3x+x)=>2x as per question we know, 2x=28/3=>2x=28/3=>x=14/3speed in still water = ½*(a+b)=>1/2*(3x+x)=>2x as per question we know, 2x=28/3=>x=14/3

 

So,

Speed upstream = 14/3 km/hr, Speed downstream 14 km/hr.

Speed of the current

=1/2[14−14/3]=14/3 kmph

 

 

 

 

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