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In the expression above, if xn#0, what is the value of S?

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In the expression above, if xn#0, what is the value of S? [#permalink] New post 18 Dec 2012, 07:13
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S=\frac{\frac{2}{n}}{\frac{1}{x}+\frac{2}{3x}}

In the expression above, if xn#0, what is the value of S?

(1) x = 2n
(2) n = 1/2
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Re: In the expression above, if xn#0, what is the value of S? [#permalink] New post 18 Dec 2012, 07:17
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S=\frac{\frac{2}{n}}{\frac{1}{x}+\frac{2}{3x}}

In the expression above, if xn#0, what is the value of S?

S=\frac{\frac{2}{n}}{\frac{1}{x}+\frac{2}{3x}}=\frac{\frac{2}{n}}{\frac{5}{3x}}=\frac{6x}{5n}

(1) x = 2n --> S=\frac{6x}{5n}=\frac{6*2n}{5n}=\frac{12}{5}. Sufficient.

(2) n = 1/2. We need the value of x to answer the question. Not sufficient.

Answer: A.
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Re: In the expression above, if xn#0, what is the value of S? [#permalink] New post 20 Dec 2013, 09:32
Hi guys,

quick question:

I started to simplify the equation by multiplying the denominator such as 2/n (x+3x/2) and did not get the same solution. What is wrong with my approach?

Thanks a lot in advance!
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Re: In the expression above, if xn#0, what is the value of S? [#permalink] New post 21 Dec 2013, 04:39
Expert's post
steilbergauf wrote:
Hi guys,

quick question:

I started to simplify the equation by multiplying the denominator such as 2/n (x+3x/2) and did not get the same solution. What is wrong with my approach?

Thanks a lot in advance!


Your approach is not clear at all. Please show your work. Thank you.
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Re: In the expression above, if xn#0, what is the value of S? [#permalink] New post 21 Dec 2013, 06:54
Hi Bunuel,

sorry for being imprecise and thanks for your quick answer.

I used the following approach:

S=\frac{\frac{2}{n}}{\frac{1}{x}+\frac{2}{3x}}

S= \frac{2}{n}(x+\frac{3x}{2})

S= \frac{2x}{n}+\frac{6x}{2n}

S= \frac{4x}{2n}+\frac{6x}{2n}=\frac{5x}{n}

Can you please tell me what is wrong with my approach?

Thanks a lot in advance.
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Re: In the expression above, if xn#0, what is the value of S? [#permalink] New post 22 Dec 2013, 05:30
Expert's post
steilbergauf wrote:
Hi Bunuel,

sorry for being imprecise and thanks for your quick answer.

I used the following approach:

S=\frac{\frac{2}{n}}{\frac{1}{x}+\frac{2}{3x}}

S= \frac{2}{n}(x+\frac{3x}{2})

S= \frac{2x}{n}+\frac{6x}{2n}

S= \frac{4x}{2n}+\frac{6x}{2n}=\frac{5x}{n}

Can you please tell me what is wrong with my approach?

Thanks a lot in advance.


The point is that reciprocal of the denominator is not x+\frac{3x}{2}.

The denominator is \frac{1}{x}+\frac{2}{3x}=\frac{3+2}{3x}=\frac{5}{3x}, thus its reciprocal is \frac{3x}{5}.
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COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Re: In the expression above, if xn#0, what is the value of S?   [#permalink] 22 Dec 2013, 05:30
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