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manhattan geometry rate problem

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manhattan geometry rate problem

by resilient » Tue Mar 25, 2008 10:18 pm
A cylindrical water tank has a diameter of 14 meters and a height of 20 meters. A water truck can fill (PIE) cubic meters of the tank every minute. How long will it take the water truck to fil the water tanhk from empty to half full.

qa is 8 hours 10 minutes. Fairly simple question EXCEPT. Volume pie r^2h = 980 and I divided this by PIE which is roughly 3. BUt solution simply splits 980 in half for the answer.

HOW DO I KNOW WHEN TO CONVERT PIE TO 3 OR JUST LEAVE IT AS 1 LIKE THIS QUESTION?
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by musicdaemon » Tue Mar 25, 2008 10:55 pm
Question asks -> what is the time for the cylinder to fill from empty to half full, So, height in this case should be 10 and not 20 ( I think you made this mistake, that is why you get 980)

Thus volume = pi*(r^2)*h
= pi*(7^2)*10
= 490pi cubic meters
Time Req = volume/Rate = (490pi)/pi = 490 min

Regarding when to convert pi in 3 (correct value 3.14), never do that until the last step. Most of the times “pi” gets cancelled by some other term, as seen above.
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EXCELLENT

by resilient » Wed Mar 26, 2008 12:08 am
Excellent reply.. I see my mistakes. I totaly forgot about converting to 3.14 but only at the end or last possible step. Its little mistakes like this that can yield many lost points.
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by gmat765 » Wed Apr 16, 2008 8:38 pm
3.1415927
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