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What is the value of s?

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Intern
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Joined: 24 Aug 2017
Posts: 8

Kudos [?]: 5 [0], given: 1

What is the value of s? [#permalink]

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New post 11 Oct 2017, 22:01
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

69% (00:59) correct 31% (01:09) wrong based on 35 sessions

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What is the value of s?

1) \(\frac{1}{s} = \frac{1}{(s+25)} + \frac{1}{(s+1)}\)
2) -1/5 is not a reciprocal of s
[Reveal] Spoiler: OA

Kudos [?]: 5 [0], given: 1

Expert Post
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Joined: 02 Aug 2009
Posts: 5214

Kudos [?]: 5860 [1], given: 117

Re: What is the value of s? [#permalink]

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New post 12 Oct 2017, 01:24
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Expert's post
khalid228 wrote:
What is the value of s?

1) \(\frac{1}{s} = \frac{1}{(s+25)} + \frac{1}{(s+1)}\)
2) -1/5 is not a reciprocal of s



Let's see the statements
1) \(\frac{1}{s} = \frac{1}{(s+25)} + \frac{1}{(s+1)}\)
\(\frac{1}{s+25}+\frac{1}{s+1}-\frac{1}{s}=0........\frac{s^2+s+s^2+25s-(s^2+26s+25)}{s(s+1)(s+25)}=0.........\)
For the fraction to be 0, numerator has to be 0..
So \(s^2-25=0\) or s=5 or s=-5
Two values possible..
Insufficient

2) -1/5 is not a reciprocal of s
s can be any value except-5
Insufficient

Combined..
Only value possible is s as 5
Sufficient

C
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Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 5860 [1], given: 117

Intern
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Joined: 24 Aug 2017
Posts: 8

Kudos [?]: 5 [0], given: 1

What is the value of s? [#permalink]

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New post 12 Oct 2017, 01:39
chetan2u I understand the concept and ideal behind it now, but could you explain to me how you went from the first equation to the second?

\(\frac{1}{s+25}+\frac{1}{s+1}-\frac{1}{s}=0.............

\frac{s^2+s+s^2+25s-(s^2+26s+25)}{s(s+1)(s+25)}=0\)

Kudos [?]: 5 [0], given: 1

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Kudos [?]: 5860 [0], given: 117

What is the value of s? [#permalink]

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New post 12 Oct 2017, 20:18
khalid228 wrote:
chetan2u I understand the concept and ideal behind it now, but could you explain to me how you went from the first equation to the second?

\(\frac{1}{s+25}+\frac{1}{s+1}-\frac{1}{s}=0.............

\frac{s^2+s+s^2+25s-(s^2+26s+25)}{s(s+1)(s+25)}=0\)



Hi..

We are actually getting all terms in equivalent form by getting the denominator same for all fractions
First take LCM of the denominator and then simplify the term by adding all fractions.


\(\frac{1}{s+25}+\frac{1}{s+1}-\frac{1}{s}=\frac{1*(s+1)*s+(s+25)*s-(s+1)(s+25)}{(s+1)(s+25)(s)}=0.............

\frac{s^2+s+s^2+25s-(s^2+26s+25)}{s(s+1)(s+25)}=0\)[/quote]
_________________

Absolute modulus :http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

Kudos [?]: 5860 [0], given: 117

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Joined: 17 Dec 2012
Posts: 623

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Location: India
Re: What is the value of s? [#permalink]

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New post 14 Oct 2017, 21:57
The second statement is a giveaway. It suggests we get two values from statement 1. Solving the first statement is also straightforward. We get 2 values for s. With statements 1 and 2, the question can be answered.

Hence C.
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Kudos [?]: 535 [0], given: 16

Re: What is the value of s?   [#permalink] 14 Oct 2017, 21:57
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