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If you see multiple addition or subtraction under the root, make sure you simplify that first and take square root of the total.

\(\sqrt{1+2-3+5-5+9} = \sqrt{9} = 3\)

However, \(\sqrt{mn} = \sqrt{m}*\sqrt{n}\)

For addition and subtraction, one can't split the terms as individual root term. And also the vice versa is not allowed(two split root terms can't be combined under one root)

For multiplication and division, one can split the terms as individual root term. Vice versa is also true.

Re: GMAT Diagnostic Test Question 2 [#permalink]
25 May 2011, 00:39

1

This post received KUDOS

MitDavidDv wrote:

I actually didn't get why you eliminated A, B, D. I think this method would be dangerous. Solving it entirely is better. Shouldn't take you more than 45 seconds if you practice a bit.

What if the question was: \sqrt{9^2+5^3+10^2+55}+\sqrt{20}

Shalom. I eliminated A, B, and D because they contain the sqrt{20} unsimplified. I am sure that solving it would be better I agree. I am only pointing out that I noticed A, B, and D could possibly be done away with using the process of elimination. The remaining two answers have the sqrt{20} broken down. If the question was \sqrt{9^2+5^3+10^2+55}+\sqrt{20} then I would consider the answer choices with the sqrt{20} simplified.

However, the answer to the question I asked is "A". \(\sqrt{9^2+5^3+10^2+55}+\sqrt{20} = 19+\sqrt{20}\)

I wouldn't advocate to guess in these simplify type of questions. Save the guessing and POE for relatively difficult questions.

But, if you are confident about your method; then please do so!!! _________________

Re: GMAT Diagnostic Test Question 2 [#permalink]
26 Nov 2009, 07:15

Made a stupid mistake and really shouldn't have since I factored 20 right away! Figured that 5 under the radical would matter and it did. Will go w/ my gut next time. _________________

Re: GMAT Diagnostic Test Question 2 [#permalink]
11 Jan 2010, 20:46

gottabwise wrote:

Made a stupid mistake and really shouldn't have since I factored 20 right away! Figured that 5 under the radical would matter and it did. Will go w/ my gut next time.

Just reworked problem. Remembered that I had to add the numbers under the radical before I could simplify anything. _________________

The first part of D, 5 times sqrt of 100, is impossible to get if you factored correctly. If you add up all three terms you should get 125. The sq. root of 125 can be broken down into the square root of (5 x 5 x 5).

Re: GMAT Diagnostic Test Question 2 [#permalink]
05 May 2011, 06:48

1

This post was BOOKMARKED

Shalom [b]Tell me if I am wrong but if I had to make an educated guess on this question I would chose E. If you breakdown the sqrt(20) that leaves 2*sqrt(5). The only possible answer would be E simply because three of the other four possible answers include the sqrt(20) unsimplified. [/b]

Re: GMAT Diagnostic Test Question 2 [#permalink]
24 May 2011, 13:58

Shalom [b]Tell me if I am wrong but if I had to make an educated guess on this question I would chose E. If you breakdown the sqrt(20) that leaves 2*sqrt(5). By using the process of elimination you can get rid of three of the four possible answers. That would leave C and E. Then if I would have had to make a choice between these two I would chose E because it is the most simplified.

Re: GMAT Diagnostic Test Question 2 [#permalink]
24 May 2011, 14:09

MitDavidDv wrote:

Shalom [b]Tell me if I am wrong but if I had to make an educated guess on this question I would chose E. If you breakdown the sqrt(20) that leaves 2*sqrt(5). By using the process of elimination you can get rid of three of the four possible answers. That would leave C and E. Then if I would have had to make a choice between these two I would chose E because it is the most simplified.

I actually didn't get why you eliminated A, B, D. I think this method would be dangerous. Solving it entirely is better. Shouldn't take you more than 45 seconds if you practice a bit.

What if the question was: \(\sqrt{9^2+5^3+10^2+55}+\sqrt{20}\) _________________

Re: GMAT Diagnostic Test Question 2 [#permalink]
24 May 2011, 20:54

I actually didn't get why you eliminated A, B, D. I think this method would be dangerous. Solving it entirely is better. Shouldn't take you more than 45 seconds if you practice a bit.

What if the question was: \sqrt{9^2+5^3+10^2+55}+\sqrt{20}

Shalom. I eliminated A, B, and D because they contain the sqrt{20} unsimplified. I am sure that solving it would be better I agree. I am only pointing out that I noticed A, B, and D could possibly be done away with using the process of elimination. The remaining two answers have the sqrt{20} broken down. If the question was \sqrt{9^2+5^3+10^2+55}+\sqrt{20} then I would consider the answer choices with the sqrt{20} simplified.