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.
Manish said:
1 decade ago
How did you evaluate 7*(1/2) ?
Jyoti said:
1 decade ago
How does 3 quarters of kilometers is converted?
Nizampatnam said:
1 decade ago
Yes Down Stream 7 1/2=15/2*60
=900/2
=450sec
=900/2
=450sec
Deepi said:
1 decade ago
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
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
Deepi said:
1 decade ago
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.
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.
Santhosh said:
1 decade ago
@sanchit : You Have done Perfect :)
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 ?
Jerry said:
1 decade ago
3/4=0.75km
0.75*1000=750km
0.75*1000=750km
Nagarjun said:
1 decade ago
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
(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
Sumathipriya said:
1 decade ago
how to find rate upstream and rate downstream?
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