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 3 of 5.
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)
Naveena said:
9 years ago
Hi, I'm a beginner for this type of problem. Can anyone explain this question for me?
Shyam Mohan said:
9 years ago
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.
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:
9 years ago
How to solve this question if the rate for going downstream is not given?
Ashoka said:
9 years ago
From the last second step 25/18 * 18/5 from where 18/5 came?
Rajesh said:
8 years ago
How 15/2 came? Explain.
Parag said:
8 years ago
How did 450 came?
Bhavuk said:
8 years ago
From where 450 has come?
Sriteja said:
8 years ago
Anyone, please explain conversion from meters to kilometers in this problem.
Tejaswini said:
8 years ago
How did 450? please explain it.
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