another practive GRE question.

[ski]

http://img57.imageshack.us/img57/6158/anotherrp0.png (http://imageshack.us)

Can someone explain how to figure this out w/o a calculator.

I can't imagine guesstimating is the best idea. This one may be basic.

PS I assume you can't use a calculator for the GRE right?

[BruceZ]

[ QUOTE ]
http://img57.imageshack.us/img57/6158/anotherrp0.png (http://imageshack.us)

Can someone explain how to figure this out w/o a calculator.

I can't imagine guesstimating is the best idea. This one may be basic.

PS I assume you can't use a calculator for the GRE right?

[/ QUOTE ]

Column A is sqrt(50) and column B is sqrt(49), so column A is greater.

[madnak]

Right.

sqrt(10) * sqrt(5) versus 7.

That's sqrt(50) versus 7. And what is 7?

7 is sqrt(49).

So, is sqrt(50) > sqrt(49)? Yes, it is.

[Prodigy54321]

it is 5*(sqrt 2)

sqrt 2 must be greater than 7/5

(7/5)^2 is 49/25 which is less than 2...so 5*(sqrt 2) > 7

although I'm sure there is an easier way /images/graemlins/tongue.gif

[John21]

multiply 5 x 10 = 50
7^2 = 49

That would work unless you need a calculator to figure 5 x 10 or 7 x 7

[hmkpoker]

Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[Prodigy54321]

[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

oh shiznat we got punk'ed

[BruceZ]

[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

That symbol means the "principal square root", which is defined to be the inverse of f(x) = x^2 for x >= 0. If you want the negative square root, you would have to put a minus sign in front of that symbol. See mathworld (http://mathworld.wolfram.com/SquareRoot.html).

[hmkpoker]

[ QUOTE ]
[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

That symbol means the "principle square root", which is defined to be the inverse of f(x) = x^2 for x >= 0. If you want the negative square root, you would have to put a minus sign in front of that symbol. See mathworld (http://mathworld.wolfram.com/SquareRoot.html).

[/ QUOTE ]

If this is true, I demand a refund in the amount of my proportional pay to math teachers throughout high school, because I am positive that I was not taught that goofy nomenclature nonsense.

Also, if this is true, I believe it is fair to say that this test is discriminatory against intelligent people /images/graemlins/smile.gif

[John21]

I still don't know why you wouldn't just square both sides of the equation to remove the sqrt(s).

[madnak]

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

That symbol means the "principle square root", which is defined to be the inverse of f(x) = x^2 for x >= 0. If you want the negative square root, you would have to put a minus sign in front of that symbol. See mathworld (http://mathworld.wolfram.com/SquareRoot.html).

[/ QUOTE ]

If this is true, I demand a refund in the amount of my proportional pay to math teachers throughout high school, because I am positive that I was not taught that goofy nomenclature nonsense.

Also, if this is true, I believe it is fair to say that this test is discriminatory against intelligent people /images/graemlins/smile.gif

[/ QUOTE ]

It's true. Think of the quadratic formula - why use the +/- if it can be either? But lots of teachers seem to screw it up. My calc book says the (radical sign) is positive, so I'm trusting that. But I wouldn't put it past the GRE to have a question with an ambiguous answer.

[carlo]

[ QUOTE ]
I still don't know why you wouldn't just square both sides of the equation to remove the sqrt(s).



[/ QUOTE ] oops-negative*positive?

[Bill Haywood]

[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

GRE does not use trick questions. I wrote questions for ETS (the GRE company) for a summer, and they would never use a question that had some pedantic gimmick.

I solved by taking 3.3 times 2.3, and guesstimating that the sum is greater than 7.

[vhawk01]

Thats like the worst imaginable way of doing it.

[greeeeeez]

[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

he is correct. the first example in my gre book is very very similar. they make a point to show you that square roots written this way can be +/-. its not really a trick question, just difficult for those who have some but not great knowledge on the subject. also, i took the gre last friday and the very first question was somewhat similar but used cube roots where its not +/-, so be prepared for both.

i got an 800 on math fwiw.

[tabako]

The way I was taught this in school is that scalars are assumed to be positive when square rooted, unless otherwise noted. For variables, the possibility of a positive and negative answer must be noted.

Odd roots obviously do not have this problem.

[chezlaw]

[ QUOTE ]
[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

he is correct. the first example in my gre book is very very similar. they make a point to show you that square roots written this way can be +/-. its not really a trick question, just difficult for those who have some but not great knowledge on the subject. also, i took the gre last friday and the very first question was somewhat similar but used cube roots where its not +/-, so be prepared for both.

i got an 800 on math fwiw.

[/ QUOTE ]
So our top maths poster says its conventionally the +ve root (that's my experience as well), someone who claims to write similar questions says its the +ve root you claim its either +ve or -ve and no-one else seems sure.

It nothing to do with how knowledgable you are about the subject and everything to do with knowing what this exam expects. They better make it very clear what's expected in which case the only problem is that the OP didn't give us all the information.

chez

[BruceZ]

[ QUOTE ]
[ QUOTE ]
Relationship cannot be determined. The sqrt of either 10 or 5 could be + or -.

[/ QUOTE ]

he is correct. the first example in my gre book is very very similar. they make a point to show you that square roots written this way can be +/-.

[/ QUOTE ]

If by +/- you mean either a positive or negative number at the same time, then you are dead wrong; however, your statement doesn't say this, and you are misinterpreting what your book is trying to tell you. I suggest that you go back and review what it says very carefully. I suspect that what it really says is that sqrt(x^2) could be either +x or –x. Note that this statement is correct, and very different from what you are claiming. It means that sqrt(x^2) = +x when x is a positive number, and sqrt(x^2) = -x when x is a negative number. It does NOT mean that it can be both of these at once, unless x=0, and it does NOT mean that sqrt(x^2) can EVER be a negative number. Note that sqrt(x^2) is a positive number in both cases, and sqrt(x^2) = |x| for real x by definition, which is always positive.

I hope that you can see the difference between this and what you have claimed above. If not, please quote exactly what your book says here, and I will explain why it is right or wrong.

Then if you are still not convinced, check out this GRE prep (http://www.wtamu.edu/academic/anns/mps/math/mathlab/int_algebra/int_alg_tut4_operations.htm) example 17 for a clear counterexample.

I already gave a link to the mathworld (http://mathworld.wolfram.com/SquareRoot.html) explanation, and here is another good one from wikipedia (http://en.wikipedia.org/wiki/Square_root).


[ QUOTE ]
its not really a trick question, just difficult for those who have some but not great knowledge on the subject.

[/ QUOTE ]

I agree, but not the way you mean.


[ QUOTE ]
i got an 800 on math WWI.

[/ QUOTE ]

Same here, many years ago. I feel less good about that now.