Test Prep2

moneyman · Posted: Sun Mar 16, 2008 6:41 am Post subject: Test Prep2

M=(4)^1/2+(4)1/3+(4)1/2 what is the value of M??

Greater than 3
Equal to 3
Between 3 and 4
Equal to 4
Greater than 4

The answer is E

camitava · Posted: Sun Mar 16, 2008 8:39 am Post subject: Re: Test Prep2

musicdaemon · Posted: Sun Mar 16, 2008 9:58 pm Post subject: Re: Test Prep2

camitava · Posted: Sun Mar 16, 2008 10:15 pm Post subject:

Hey musicdaemon, what a catch man! Good catch, indeed! But I would like to say here that generally this type of ambiguous Qs are not asked in GMAT. I agree I missed the issue mentioned by u ...

smushkas · Posted: Mon Mar 17, 2008 8:53 am Post subject:

Hey guys,

Just a quick comment. Original question was like, see the link, please.

http://www.beatthegmat.com/gmatprep-ps-t9183.html#36723

musicdaemon · Posted: Mon Mar 17, 2008 10:14 am Post subject:

camitava · Posted: Mon Mar 17, 2008 10:40 am Post subject:

musicdaemon · Posted: Mon Mar 17, 2008 8:18 pm Post subject:

Amitava,
I guess My basics in quant are still in place.

Sqrt of any number will have two values one -ve and one +ve

apply the reverse logic:

(-2)^2 = 4 & (2)^2 =4

Take sqrt on both sides now,

-2=sqrt(4) & 2 = sqrt(4)

Thus, sqrt(4) = +2 and -2

Prove me wrong!!!

camitava · Posted: Mon Mar 17, 2008 8:41 pm Post subject:

musicdaemon · Posted: Mon Mar 17, 2008 8:54 pm Post subject:

Amitava,
I don't have an iota of doubt on this.

The answer choices for this question are ambiguous.

gabriel · Posted: Mon Mar 17, 2008 10:29 pm Post subject:

Actually Amitava is right, the sqrt of a number until unless mentioned should be considered positive. While you are right that any integer has 2 roots, we consider only the positive root (the principal root) for solving problems such as these. So Amitava's answer is right i.e m>4. There is no ambiguity in the answer choices.

Do a google search on "principal square root" and you will find articles on why this is so.

Regards

resilient · Posted: Mon Mar 17, 2008 11:44 pm Post subject: clarification

FIrst, all you guys are great at catching such subtle details. I am a bit confused now, I see Mr. Daemon's point but see moderators point also. For the sake of the exam, are we considering all roots positive? I believe this is what is taught in the manhattan gmat book also.

AS for the original question, I think the original poster is hurting from understanding that all fractional exponents are treated as roots. I had to make a flash card on this to commit it to memory. Recommendations to you also.

gabriel · Posted: Mon Mar 17, 2008 11:52 pm Post subject: Re: clarification

musicdaemon · Posted: Tue Mar 18, 2008 12:20 am Post subject:

Gabriel,
For discreet values given as choices, of simple functions, we can use the principle sq root. But, when the range of values is required then you may have to use both the values. And that is what is the case in the given problem.

i guess we have to get it by heart - to use +ve root for GMAT unless required specifically.

suman2424 · Posted: Wed Mar 19, 2008 11:20 am Post subject:

Yes by convention, sqrt(x) is always positive. Because of this, the answer must be greater than 4.