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26 Dec 2021, 22:04
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Difficulty:
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Question Stats:
10% (01:54) correct
90%
(01:31)
wrong
based on 73
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A 100 meter wide river can be crossed straightly, in 4 minutes when there is no stream and 5 minutes when there is stream. What is the speed of the stream ?
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
26 Dec 2021, 22:31
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Mugdho
A 100 meter wide river can be crossed straightly, in 4 minutes when there is no stream and 5 minutes when there is stream. What is the speed of the stream ?
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
This is what the question means - if you cross the 100 m side river directly in still water, you would take 4 mins.
So your speed (without any external influence) = 100/4 = 25 meter/min
But the stream sways you away every moment as you swim and hence makes you cover extra distance and makes you travel diagonally (as shown in the diagram)
So distance covered in 5 mins = 25*5 = 125 meters
Attachment:
Screenshot 2021-12-27 at 10.57.27.png [ 19.37 KiB | Viewed 2852 times ]
This is a right triangle of sides ratio 3-4-5 so the third side is 75 meters (distance between point of 'still water' and point of 'with stream').
Hence the stream moved 75 meters in 5 mins. Imagine one water molecule that stuck to you when you entered the river and then acted upon you till you reached the other end. That molecule travelled 75 metres in 5 mins.
Speed of the stream = 75/5 = 15 meters/min
Answer (B)
27 Dec 2021, 06:02
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KarishmaB
Mugdho
A 100 meter wide river can be crossed straightly, in 4 minutes when there is no stream and 5 minutes when there is stream. What is the speed of the stream ?
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
a) 10 meter/minute
b) 15 meter/minute
c) 20 meter/minute
d) 5 meter/minute
e) None
Posted from my mobile device
This is what the question means - if you cross the 100 m side river directly in still water, you would take 4 mins.
So your speed (without any external influence) = 100/4 = 25 meter/min
But the stream sways you away every moment as you swim and hence makes you cover extra distance and makes you travel diagonally (as shown in the diagram)
So distance covered in 5 mins = 25*5 = 125 meters
Attachment:
Screenshot 2021-12-27 at 10.57.27.png
This is a right triangle of sides ratio 3-4-5 so the third side is 75 meters (distance between point of 'still water' and point of 'with stream').
Hence the stream moved 75 meters in 5 mins. Imagine one water molecule that stuck to you when you entered the river and then acted upon you till you reached the other end. That molecule travelled 75 metres in 5 mins.
Speed of the stream = 75/5 = 15 meters/min
Answer (B)
One doubt in the solution: if someone swims straightly then he will go 125 meter in 5 minutes in the still water.
In the second case, when he is going with his own speed + stream speed, he is still going 125 meter in 5 minutes.
How is this possible ?
