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Boat/Rowing Problem !!

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Boat/Rowing Problem !!

by Taran » Sat Dec 11, 2010 10:56 pm
Q - A man can row at 10km/hr in still water. If it takes a total of 5 hours for him to go to a place 24 km away and return, then find the speed of the water current in km/hr.

A - 2
B - 3.5
C - 5
D - 7.2
E - 8
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by goyalsau » Sun Dec 12, 2010 12:39 am
Taran wrote:Q - A man can row at 10km/hr in still water. If it takes a total of 5 hours for him to go to a place 24 km away and return, then find the speed of the water current in km/hr.

A - 2
B - 3.5
C - 5
D - 7.2
E - 8
We can plug in answer choices,

10 + 2 = 12 km/hour

24/12 = 2 hour

10 - 2 = 8 km/hour

24/8 = 3 hour

2 + 3 = 5 hours

Option A
Saurabh Goyal
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by Taran » Sun Dec 12, 2010 12:50 am
Thanks goyalsau !!!

Putting in the answers was a good way to go about here, but what if the correct answer was E. I would have used lot of time to come to check option E. Did you pick to test A randomly or was there any intuitive reason?

Also, how would you solve this the normal way (w/o putting the values)?
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by goyalsau » Sun Dec 12, 2010 1:54 am
Taran wrote:Thanks goyalsau !!!

Putting in the answers was a good way to go about here, but what if the correct answer was E. I would have used lot of time to come to check option E. Did you pick to test A randomly or was there any intuitive reason?

Also, how would you solve this the normal way (w/o putting the values)?
Let the speed of water we x

While with the water speed must be 10 + x

while coming back it must be 10 - x

total time is 5 hours.

24/(10+x ) + 24/ ( 10 - x ) = 5

10 + x + 10 - x = 100 - x^2 ( 5/24 )

480 = 500 - 5x^2

x ^2 = 4

x = 2

Speed of water is 2 km/hour
Saurabh Goyal
[email protected]
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by Taran » Sun Dec 12, 2010 3:01 am
ahhh !!!! :)

Sometimes simple things appear tough !!! Thanks a lot....
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