Aptitude - Boats and Streams - Discussion
Discussion Forum : 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:
minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:Answer: Option
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.
Discussion:
42 comments Page 1 of 5.
M Ganesh said:
5 years ago
3 Quarters means-3/4th km.
Time taken for upstream- 45/4 min.
Time taken for downstream-15/2 min.
We need to calculate upstream and downstream.
Upstream-3/4/45/4*60.
= 4km/hr.
Downstream=3/4/15/2*60.
=6km/hr.
Sb - sw = 4.
Sb + sw = 6.
Solving this eqn we will get;
Sb = 5km.
Time taken for upstream- 45/4 min.
Time taken for downstream-15/2 min.
We need to calculate upstream and downstream.
Upstream-3/4/45/4*60.
= 4km/hr.
Downstream=3/4/15/2*60.
=6km/hr.
Sb - sw = 4.
Sb + sw = 6.
Solving this eqn we will get;
Sb = 5km.
(11)
Laxman Pawar said:
5 years ago
When we cross multiply, we should get as 10.
15/2*3/4 = 10,
45/4*4/3 = 15,
10-15 = 5,
So, the Answer is 5.
15/2*3/4 = 10,
45/4*4/3 = 15,
10-15 = 5,
So, the Answer is 5.
(4)
Ansh said:
6 years ago
@All.
Here, the speed of man is asked then why you have calculated the rate of water? Please explain me.
Here, the speed of man is asked then why you have calculated the rate of water? Please explain me.
(2)
Dhakshina said:
10 years ago
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.
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.
(2)
Dilip Kumar said:
5 years ago
@MGanesh.
How did you take 3/4/15/2*60?
How did you take 3/4/15/2*60?
(1)
Malay said:
6 years ago
Don't understand this sum, how to find the speed of man?
(1)
Sanchit said:
1 decade ago
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 ?
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 ?
(1)
Ganga said:
6 years ago
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.
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.
(1)
Hari Gudapati said:
7 years ago
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.
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.
(1)
Prachiti said:
9 years ago
How to solve this question if the rate for going downstream is not given?
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