Aptitude - Boats and Streams - Discussion

1. 

A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.

[A]. 2 hours
[B]. 3 hours
[C]. 4 hours
[D]. 5 hours

Answer: Option C

Explanation:

Speed downstream = (13 + 4) km/hr = 17 km/hr.

Time taken to travel 68 km downstream = 68 hrs = 4 hrs.
17


Balaji said: (Mar 18, 2011)  
In the question they given the data that

speed of boat 13 km/hr and speed of stream is 4 km/hr

and they asked us to solve the time taken by the boat in down stream for a distance of 68 kms.

we know as per the formula down stream means speed of boat + speed of stream

therefore,
down stream = 13+4=17 km/hr
as per the problem we got to find time taken by boat to travel a distance of 68km down stream.

we have formula that, time=distance/speed
=68/17
=4 hours

Manasa said: (Jun 12, 2011)  
Thanks Balaji.

Geetha said: (Jun 16, 2011)  
Thanks for your explanation.

Anshu said: (Apr 4, 2012)  
Total speed during downstream,
Speed = 13kmph + 4 kmph = 17 kmph.
Time = distance / speed = 4 hours.
Hope this helps!

Arun.D said: (Jun 3, 2013)  
Speed of boat in still water = 13km/hr.
Speed of the stream = 4km/hr.
Time taken by the boat to go 68 km downstream = ?

Speed of boat in downstream = (13+4)km/hr.
= 17km/hr.

Time = distance/speed.
= 68/17hr.
= 4hr.

Akash U. said: (Jan 25, 2014)  
(Total speed)downstream = Speed of boat + Speed of stream.

Time = Distance/speed.

Wangdeep Tamang said: (Mar 22, 2014)  
Speed in Still water = 13 km/h.
Speed of the stream = 4 km/h.

Downstream = 13+4 = 17km (speed in Still water + speed of the stream).
Time Take = 68/17 = 4 hrs.

Manikyam said: (Apr 7, 2015)  
How to know particularly which formula to use whether downstream or upstream? Bit confusing?

Somya said: (May 27, 2015)  
It is given in the question to find time taken to go 68 km downstream.

Srikanth said: (Jun 24, 2015)  
Downstream speed = a.
Upstream speed = b.

Stream speed = 1/2 (a-b)----Formula.
Boat speed = 1/2 (a+b)-----Formula.

Given boat speed = 13.
Stream speed = 4.

So 1/2(a+b)+1/2(a-b) = 13+4.

==> a=7.

Given D = 68km.

D = S*T.
Ta = D/Sa.

=>68/17.

=>4.

So time taken by the boat to go 68 km downstream is 4 hrs.

Prassanna.S said: (Aug 19, 2015)  
Thanks for giving the correct answer.

V!Cky said: (Sep 6, 2015)  
Use Speed = Distance /Time formula.

Still in water u+v = 13+4 = 17.

68/17 = 4 km/hr.

Roshan said: (Sep 12, 2015)  
Still water speed + Boat speed = Total speed (down stream).

Time = Distance/Speed.

Praveen said: (Oct 14, 2015)  
Still water means? How it has speed?

Chetan said: (Dec 12, 2015)  
It means speed of boat in still water is 13 km/h.

Laxmidhar said: (Dec 16, 2015)  
Sp of down stream = (13+4) = 17.

Time taken = 68\17 = 4 hr.

Csharad said: (Mar 19, 2016)  
Here any short cut method for this?

Kiruthika said: (Jun 28, 2016)  
Given:

Speed in still water U = 13 km/hr,

Speed of stream V = 4 km/hr,

Distance = 68 km,

Time = ?

Solution:

Time = distance / U+V(downstream speed)

=> 68/17,

=> 4 hour.

Sivananda said: (Jul 7, 2016)  
Super explanation @Balaji. Thanks.

Avijit Das said: (Jul 24, 2016)  
Appropriate explanation, Thanks to all.

Honey said: (Aug 10, 2016)  
Good explanation, Thanks to all.

Gaurank Verma said: (Aug 25, 2016)  
Since ship is going downstream,

Hence,
Resultant speed = 13 + 4 = 17 km/h.

Now,

Time = distance / speed.
==> Time = 68/17 = 4hours.

Therefore, the boat will take 4 hrs. To go 68 km downstream.

Narayana Reddy said: (Sep 23, 2016)  
Thanks for providing the answer and explanation.

Raj said: (Jan 19, 2017)  
Hi, please give me a solution for this question.

"A man can row 8 kms in still water. If in a river flowing at 2 km an hour, it takes him 24 minutes to row to a place and come back, how far of is this place?"

A.Santhosh said: (Apr 2, 2017)  
Boat -> a kmph& stream-> b kmph

A= boat speed at still water
B= water speed=rate of current=stream speed.

Along with the flow, Dss(downstream speed) = a+b,
Againist with the flow, Uss(upstream speed) = a-b.

So, a + b = 13 + 4 = 17,
Distance = 68 km,
Time = Dist/Uss,
T = 68/17 = 4hrs.

Vadivel said: (Apr 6, 2017)  
Thaks for explaining the answer friends.

Birla Jyothi Swaroop said: (Apr 27, 2017)  
Perfect Explanation, thank @Santhosh.

Ardhendu Sikdar said: (Jun 17, 2017)  
13+4 = 17km/hr.
Now, 48/17 = 4hr.

Mythu said: (Jul 26, 2017)  
Thanks for all your explanations.

Elizabath said: (Mar 13, 2018)  
Give a clear explanation to get it.

Sheetul said: (Sep 9, 2018)  
Thank you so much @Balaji.

Gauravbagul said: (Nov 18, 2018)  
13+4 = 17km/hr,
For 1 hour he goes 17 km.
Then for 68 km he takes 4 hrs.

Md Abdul Khabir said: (Jul 30, 2019)  
Thank you all for explaining it clearly.

Venky said: (Aug 1, 2019)  
Thanks to all for giving an explanation.

Bhushan Roy said: (Sep 6, 2019)  
Thanks for the nice explanation.

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