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# m06 q30

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Manager
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18 Nov 2008, 19:44
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What is the value of the following expression: $$6x^2 + 9y^2?$$

1. $$x = 2$$
2. $$6y^2 + 4x^2 = 22$$

[Reveal] Spoiler: OA
B

Source: GMAT Club Tests - hardest GMAT questions

Statement 1 provides us with value of x but it is insufficient to answer the whole question

Statement 2 provides us with necessary information: we need to multiply the second statement times 1.5 and we will get our result: $$33 = 9y^2 + 6x^2$$

How is x = 2 no sufficient? If we know the value for x we can solve for y and then add the two.

Thank you.
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18 Nov 2008, 22:05
3
KUDOS
When the question says "What is the value of..." the question is asking if we have enough information to determine a single value. There are 2 variables in the equation provided (x and y) and S1 only gives us a value for x. The equation is not equal to anything, ti's just an equation. IF THE QUESTON HAD provided the equation of $$6x^2 + 9y^2 = 33$$, then providing us with the value of a single variable WOULD be enough to find the value of y and therefore would be sufficient, but this information is still missing. Look at every problem as if it has 2 varaibles.

a = b

Sometimes we know one variable, such as a = 2. If a = 2, then b = 2. If we have a more complext problem, we have $$a^2 + b = c$$. Now we have 3 variables. This is similar to the equation given. While the question isn't written with that third variable visible, it is present. Its the variable we're trying to solve for. It $$6x^2 + 9y^2 = z$$ and we need to find z. So anytime you have 3 variables, in order to solve for the entire equation to a single value, you need to know the value of AT LEAST 2 of those variables. [There are exceptions to this, but as a general rule, knowing the information necessary to solve the equation is a vital step in doing Data Sufficiency questions.]

smarinov wrote:
What is the value of the following expression: $$6x^2 + 9y^2?$$

1. $$x = 2$$
2. $$6y^2 + 4x^2 = 22$$

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient

Statement 1 provides us with value of x but it is insufficient to answer the whole question

Statement 2 provides us with necessary information: we need to multiply the second statement times 1.5 and we will get our result: $$33 = 9y^2 + 6x^2$$

How is x = 2 no sufficient? If we know the value for x we can solve for y and then add the two.

Thank you.

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06 Aug 2010, 06:53
Ans - B. an easier question!!!!
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07 Aug 2010, 11:08
Multiply the question by (6/4), we will get the ans.
So Ans will be " B "
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31 Aug 2010, 15:42
smarinov wrote:
What is the value of the following expression: $$6x^2 + 9y^2?$$

1. $$x = 2$$
2. $$6y^2 + 4x^2 = 22$$

[Reveal] Spoiler: OA
B

Source: GMAT Club Tests - hardest GMAT questions

IMO B

A - no data for y
B - equation is a multiple of equation in qustion
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09 Aug 2011, 07:38
smarinov, you could solve for Y ONLY and ONLY provided that you knew the original equation equals zero or any other number. Yes, you know x=2. Just imagine the other side of the equation is 0, you say then you can solve for y and y=square root of 24/9

What if the original equation was 6x^2 + 9y^2=6 ?? Actually the question is asking us to find this 6. Then substituting 2 for x, y would equal 2, which is different from the Y we got by assuming zero is on the other side of the equation.

Hope it helps
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29 Aug 2012, 07:37
Not sure if this was indeed a very hard DS question. Was relatively straight forward that statement (ii) is sufficient. I had to re-check if I was missing anything with statement (i) since (ii) was rather obvious.

The answer I chose was B.
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13 Aug 2013, 06:43
Statement 1: Useless. We have no information about y
Statement 2: Can be reduced to 2x^2 + 3y^2 = 11. The equation in the question stem is fairly similar to this one ----> by multiplying the equation in statement 2 by 3 we end up with the equation in the stem. Therefore, it must also equal 33. Sufficient.

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13 Aug 2013, 08:45
smarinov wrote:
What is the value of the following expression: $$6x^2 + 9y^2?$$

1. $$x = 2$$
2. $$6y^2 + 4x^2 = 22$$

S1 doesn't tell you anything about y, eliminate A, D.
If you just factor out the original question and S2 you can form a ratio between the 2, and thus get an exact value. Correct answer is B.
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13 Aug 2013, 17:16
It's basic algebra; an expression is different than an equation.

"An equation contains an equal sign, expressions do not. An expression, even one that contains variables, represents a value. Even if you don't know that value, nothing you do to an expression can change its value." mgmat
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13 Aug 2013, 20:25
B it is.

Simplify B and you will get 2x^2 + 3y^2 =11. Multiply this by 3 and you get the required equation.:D
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13 Aug 2013, 23:54
pretty simple.

B it is.
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29 Jul 2014, 05:39
option one is not sufficient as value of x is not known. option two is sufficient to answer the question.By solving original equation.
Re: m06 q30   [#permalink] 29 Jul 2014, 05:39
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# m06 q30

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