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If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi

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Math Revolution GMAT Instructor
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If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi  [#permalink]

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New post 17 Oct 2017, 03:27
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A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

57% (02:22) correct 43% (02:36) wrong based on 76 sessions

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[GMAT math practice question]

If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the following options?

A. 0.01
B. 0.002
C. 0.02
D. 0.003
E. 0.03

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Re: If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi  [#permalink]

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New post 17 Oct 2017, 08:03
MathRevolution wrote:
[GMAT math practice question]

If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the following options?

A. 0.01
B. 0.002
C. 0.02
D. 0.003
E. 0.03



0.010<x-√5<0.011........ basically means x-√5~0....x~√5...

Let's see the equation now..
\(\frac{1}{√5}-\frac{1}{x}=\frac{x-√5}{x√5}=\frac{0.010}{√5*√5}=0.002\)

B
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Re: If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi  [#permalink]

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New post 19 Oct 2017, 00:03
=>

1/√5-1/x = x-√5/x√5

From 0.010<x-√5<0.011, we have 0.010 + √5<x <0.011 + √5.
We have 1/0.010+ √5 < 1/x < 1/0.011+ √5 or 1/0.010√5+5 < 1/x√5 < 1/0.011√5+5.
0.010/0.010√5+5 < x-√5/x√5 < 0.011/0.011√5+5.
The approximation of x-√5/x√5 is 0.01/5=0.002

Thus, the answer is B.


Answer: B
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Re: If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi  [#permalink]

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New post 14 Nov 2017, 06:35
1
chetan2u wrote:
MathRevolution wrote:
[GMAT math practice question]

If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the following options?

A. 0.01
B. 0.002
C. 0.02
D. 0.003
E. 0.03



0.010<x-√5<0.011........ basically means x-√5~0....x~√5...

Let's see the equation now..
\(\frac{1}{√5}-\frac{1}{x}=\frac{x-√5}{x√5}=\frac{0.010}{√5*√5}=0.002\)

B


Hi Chetan if x is approx √5 then how did we get .010 in the numerator.
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Re: If 0.010<x-√5<0.011, approximation of 1/√5-1/x is which of the followi &nbs [#permalink] 14 Nov 2017, 06:35
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