# Aptitude - Boats and Streams - Discussion

### Discussion :: Boats and Streams - General Questions (Q.No.12)

12.

A man can row three-quarters of a kilometre against the stream in 11 minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:

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

Explanation:

We can write three-quarters of a kilometre as 750 metres,

and 11 minutes as 675 seconds.

 Rate upstream = 750 m/sec = 10 m/sec. 675 9

 Rate downstream = 750 m/sec = 5 m/sec. 450 3

 Rate in still water = 1 10 + 5 m/sec 2 9 3

 = 25 m/sec 18

 = 25 x 18 km/hr 18 5

= 5 km/hr.

 Gulam said: (Jun 21, 2010) how to find it minutes to millisecond plz reply me Thanks

 Mohan said: (Dec 25, 2010) How can we find the value for Rate Upstream and Rate downstream reply plz /....

 Sumathipriya said: (Jan 7, 2011) how to find rate upstream and rate downstream?

 Nagarjun said: (Jan 11, 2011) rate of upstream is equal to speed of boat in upstream..say->A (and) rate of downstream is equal to speed of boat in downstream..->B speed of boat in still water = 1/2(A+B)...say->X speed of stream or rate of stream = 1/2(A-B)...say->Y then speed of boat in downstream = X+Y speed of boat in upstream = X-Y

 Jerry said: (Jun 28, 2011) 3/4=0.75km 0.75*1000=750km

 Sanchit said: (Nov 6, 2011) Distance=3/4km time taken upstream=11 1/4 min= 45/4min time taken upstream (in hours)=45/48*1/60=3/16 hrs speed upstream = distance (km)/time (in hours) =3/4 * 16/3= 4kmph time taken downstream = 7 1/2 = 15/2 min time taken downstream (in hrs) = 15/2*1/60=1/8 hrs speed downstream = distance/time = 3/4*8 = 6 kmph now, speed in still water = 1/2* (4+6) = 10/2 = 5 kmph Isn't it easier ?

 Santhosh said: (Nov 22, 2011) @sanchit : You Have done Perfect :)

 Deepi said: (Feb 5, 2012) Rate of upstream and rate of downstream means speed of upstream and speed of downstream From the formula Distance=time*speed rate of upstream=Distance/time Here they given as three quarters of km that is 3/4 and minutes from that we can find the speed in m/sec. So totally solution comes in the form of m/sec to covert the m/sec in km/h we need to multiply 18/5.

 Deepi said: (Feb 5, 2012) To convert mints to seconds just multiply by 60. to convert mints to hour just divide by 60. here 11 1/4 mint (11*4+1) 45/4 To convert 45/4*60=675

 Nizampatnam said: (Oct 12, 2012) Yes Down Stream 7 1/2=15/2*60 =900/2 =450sec

 Jyoti said: (Jul 27, 2013) How does 3 quarters of kilometers is converted?

 Manish said: (Jul 27, 2013) How did you evaluate 7*(1/2) ?

 Kishor said: (Aug 5, 2013) Downstream : Upstream ................................................... Distance(D) 3/4 x 1 km : 3/4 x 1 km Time(T) 15/2 x 60 hr : 45/4 x60 hr Speed(D/T) (3/4 x1)/(15/2 x60)=6 : (3/4 x1)/(45/4 x60)=4 Speed of man in still water = (6+4)/2 = 5 km/hr.

 Fahmi said: (Dec 28, 2013) We can do it more easy way. (3/4) * (4/45) *60 = 4 km. (3/4) * (2/15) *60 = 6 km. 1/2 (4+6) km = 5 km.

 Neelam said: (Apr 1, 2014) How we find downstream time as it is not mention in the question?

 Sunil said: (Apr 13, 2014) How did you find rate of downstream ?

 Bijendra Singh said: (Jul 24, 2014) Downstream time is given there 7 1/2 so it is 15/2*60. i.e. 900/2 = 450

 Nikul Rana said: (Nov 1, 2015) Let we assume the speed of man in still water = X kmph; And the speed of water current = Y kmph; So, The speed downstream = X+Y; And the speed against the stream = X-Y; Therefor we can say that X-Y = (3/4)/(45/4) = 4; X-Y = 4.....(1); And X+Y = (3/4)/(15/2) = 6; X+Y = 6.....(2); So that we get X = 5; //The speed of the man in still water.

 Buny said: (Jan 1, 2016) How to find time of download stream? How it is calculated 15/2?

 Sudarshan said: (Jan 23, 2016) Man Speed = 1/2 (Upstream Speed + Downstream Speed). = 1/2 (750*4/45*60 + 750*2/15*60). = (1/2)*(750/60)(2/15)( 2/3 + 1). = (750*2/2*60*15) * (5/3). = 25/18 meters/sec. = (25/18)*(18/5) Km/hr. = 5 Km/hr.

 Dhakshina said: (Jan 26, 2016) Let us consider distance as 3/4 km. Upstream speed is 45/4. Speed travelled is d/t. So (3/4)/(45/4)*1/60 (convert this into hours) = 4 km/hr. Downstream speed is 15/2. Speed travelled is d/t therefore (3/4)/(15/2)*1/60 = 6 km/hr. Therefore to find the speed of still water (Upstream + Downstream)/2 = (4+6)/2 = 5 km/hr.

 Naveena said: (Jun 11, 2016) Hi, I'm a beginner for this type of problem. Can anyone explain this question for me?

 Shyam Mohan said: (Jul 2, 2016) Step 1 - find the value of (3/4) / (45/4 * 60) Answer = 4. Step 2 - find the value of (3/4) / (15/2*60) Answer = 6. => 4 and 6 are the total speed of the man in downstream's and upstream's respectively. Step 3 - (4 + 6) /2 Answer = 5. Taking the average of the total speed gives you the speed of the man in the still water.

 Prachiti said: (Oct 13, 2016) How to solve this question if the rate for going downstream is not given?

 Ashoka said: (Jan 17, 2017) From the last second step 25/18 * 18/5 from where 18/5 came?

 Rajesh said: (May 31, 2017) How 15/2 came? Explain.

 Parag said: (Jun 27, 2017) How did 450 came?

 Bhavuk said: (Nov 13, 2017) From where 450 has come?

 Sriteja said: (Dec 9, 2017) Anyone, please explain conversion from meters to kilometers in this problem.

 Tejaswini said: (Feb 7, 2018) How did 450? please explain it.

 Chan said: (Apr 4, 2018) 1000 Meters = 1 KM. 3600 seconds = 1 Hour. So to convert meters into KM you need to divide that number by 1000 and similarly to convert seconds into Hour you need to divide that number by 3600. 3/4th of a KM = 750 meters, 11 1/4 minutes = 45/4 minutes = convert to seconds = 45/4 * 60 = 675 seconds. Now, convert meters/seconds into km/hrs like the below; 750/1000 ------------ 675/3600 which is equal to; 750/675 * 3600/1000 = 4 km/hr = Speed of upstream. Similarly, calculate for downstream and then take an average of the sum to get the answer.

 Chan said: (Apr 4, 2018) 1000 Meters = 1 KM. 3600 seconds = 1 Hour. So to convert meters into KM you need to divide that number by 1000 and similarly to convert seconds into Hour you need to divide that number by 3600. 3/4th of a KM = 750 meters, 11 1/4 minutes = 45/4 minutes = convert to seconds = 45/4 * 60 = 675 seconds. Now, convert meters/seconds into km/hrs like the below; 750/1000 ------------ 675/3600 which is equal to; 750/675 * 3600/1000 = 4 km/hr = Speed of upstream. Similarly, calculate for downstream and then take an average of the sum to get the answer.

 Cidhu said: (Aug 4, 2018) thank u @Sanchit

 Hari Gudapati said: (Aug 15, 2018) First, we convert minutes to hours i.e, 11 1/4 min to 45/4*60 hrs also 7 1/2 min to 15/2*60 hrs. Apply formula speed = distance/ time (km/hr). Rate upstream = 3/4 x 4x60 / 45 = 4 km/hr. Rate downstream = 3/4 x 8/1 = 6 km/hr. The speed of a man in still water = 1/2(4+6)= 5 km/hr.

 Chulbul Sing said: (Nov 23, 2018) How come 450? Please explain.

 Rakesh said: (Jan 17, 2019) How come to down stream? Anyone help me to get it.

 Ganga said: (May 21, 2019) Here,we r asked to find ' speed of the man in still water. It can be given as (u+v)/2.....i.e.,u->upstream speed & v-> downstream speed... To find 'u': Upstream speed = distance/time (here, time in min can be converted into hrs) u=(3/4)/(3/16) u=4 km/hr. Like abv, find v v=(3/4)/(1/8), v= 6 km/hr. Atlast, speed of the man in still water = (u+v)/2 = (4+6)/2 = 5 km/hr.

 Ansh said: (Aug 7, 2019) @All. Here, the speed of man is asked then why you have calculated the rate of water? Please explain me.

 Malay said: (Apr 5, 2020) Don't understand this sum, how to find the speed of man?