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# M19-27

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Math Expert
Joined: 02 Sep 2009
Posts: 43315

Kudos [?]: 139337 [0], given: 12786

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16 Sep 2014, 00:06
Expert's post
4
This post was
BOOKMARKED
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Difficulty:

15% (low)

Question Stats:

77% (00:30) correct 23% (00:25) wrong based on 126 sessions

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$$\frac{1}{\sqrt{51}}$$ is between:

A. 0 and $$\frac{1}{9}$$
B. $$\frac{1}{9}$$ and $$\frac{1}{7}$$
C. $$\frac{1}{7}$$ and $$\frac{1}{6}$$
D. $$\frac{1}{6}$$ and $$\frac{1}{5}$$
E. $$\frac{1}{5}$$ and $$\frac{1}{2}$$
[Reveal] Spoiler: OA

_________________

Kudos [?]: 139337 [0], given: 12786

Math Expert
Joined: 02 Sep 2009
Posts: 43315

Kudos [?]: 139337 [0], given: 12786

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16 Sep 2014, 00:06
Official Solution:

$$\frac{1}{\sqrt{51}}$$ is between:

A. 0 and $$\frac{1}{9}$$
B. $$\frac{1}{9}$$ and $$\frac{1}{7}$$
C. $$\frac{1}{7}$$ and $$\frac{1}{6}$$
D. $$\frac{1}{6}$$ and $$\frac{1}{5}$$
E. $$\frac{1}{5}$$ and $$\frac{1}{2}$$

Because $$\sqrt{49} = 7 \lt \sqrt{51} \lt \sqrt{81} = 9$$, $$\frac{1}{\sqrt{51}}$$ is between $$\frac{1}{9}$$ and $$\frac{1}{7}$$.

_________________

Kudos [?]: 139337 [0], given: 12786

Intern
Joined: 21 Dec 2016
Posts: 12

Kudos [?]: 6 [0], given: 4

Location: United Kingdom
Concentration: Strategy
Schools: LBS, Imperial '20, LBS
GMAT 1: 680 Q45 V38
GPA: 3.41

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16 Jan 2017, 13:38
I might be being stupid here but is it not also between 0 and 1/9?

Kudos [?]: 6 [0], given: 4

Intern
Joined: 16 Jan 2017
Posts: 4

Kudos [?]: 10 [0], given: 1

Location: United States
GMAT 1: 730 Q49 V41
GPA: 3.6

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16 Jan 2017, 14:32
sefwow wrote:
I might be being stupid here but is it not also between 0 and 1/9?

No, Because $$\frac{1}{\sqrt{51}}$$ is bigger than $$\frac{1}{9}$$.

Kudos [?]: 10 [0], given: 1

Intern
Joined: 04 Jun 2017
Posts: 8

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

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29 Aug 2017, 15:04
The key to this question is to not be too worried about knowing the precise square root or decimal of a number, but to be able to approximate and detect what is unnecessary in the problem, which in this case the problem tries to throw off the test taker by adding in reciprocals.

The question simply asks to determine what two numbers is 1/$$\sqrt{51}$$ between. To make the problem simpler, dumb down the question and focus only on $$\sqrt{51}$$ and not 1/$$\sqrt{51}$$. We know that $$\sqrt{51}$$ is between $$\sqrt{49}$$ and $$\sqrt{64}$$; therefore,
7 < $$\sqrt{51}$$ < 8.

Since 1/$$\sqrt{51}$$ will yield a smaller fraction due to a larger number in the denominator, 1/$$\sqrt{51}$$ is smaller than 1/7 and larger than 1/8.

Looking at the answer choice, the only number smaller than 1/8 is 0 and 1/9. This leaves us with answer choices A and B.

Because we deduced that 1/$$\sqrt{51}$$ is smaller than 1/7 and larger than 1/8, we know that 1/$$\sqrt{51}$$ is larger than 1/9 but smaller than 1/7. The answer is B.

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

Re: M19-27   [#permalink] 29 Aug 2017, 15:04
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# M19-27

Moderators: chetan2u, Bunuel

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