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 4 of 5.
Chan said:
7 years ago
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.
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:
7 years ago
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.
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:
7 years ago
thank u @Sanchit
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)
CHULBUL SING said:
7 years ago
How come 450? Please explain.
Rakesh said:
7 years ago
How come to down stream? Anyone help me to get it.
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)
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)
Malay said:
5 years ago
Don't understand this sum, how to find the speed of man?
(1)
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)
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