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square roots & decimal

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square roots & decimal

by dwilliams05 » Thu Apr 23, 2009 2:02 pm
Ran across a problem similar to this and wanted to know if anyone had a "trick" to answer this type of question?

Q: What is the approx value of sqrt[(.81) + (.05) + (.72) / (.003)]?

There is no answr solution but I'd like to know a fast method for solving questions types like this (i know its simple math so please forgive me for asking such a novie question).

Thanks
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Re: square roots & decimal

by Stuart@KaplanGMAT » Thu Apr 23, 2009 2:09 pm
dwilliams05 wrote:Ran across a problem similar to this and wanted to know if anyone had a "trick" to answer this type of question?

Q: What is the approx value of sqrt[(.81) + (.05) + (.72) / (.003)]?

There is no answr solution but I'd like to know a fast method for solving questions types like this (i know its simple math so please forgive me for asking such a novie question).

Thanks
Fastest way to do it is to simplify the expression:

sqrt[(.81 + .05 + .72)/(.003)]

sqrt[(1.58)/(.003)]

multiply by 1000/1000 to get rid of the decimals:

sqrt[1580/3]

sqrt[530ish]

weird number (and very unlikely to appear in a real GMAT question), but if we know that 20^2 is 400 and 25^2 is 625, we look for an answer between 20 and 25.
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Junior | Next Rank: 30 Posts
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by dwilliams05 » Thu Apr 23, 2009 2:36 pm
Thanks Stuart. It's similar to a real test question. In fact it was one of the first 10. I don't know why I panicked when I saw this on? Went thru the math several times and couldnt figure out where my mistake was. I also wasted time checking, re-checking, and re-checking again. I finally just moved on out of frustration but am sure I missed it.
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