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M70-35

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M70-35  [#permalink]

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New post 04 Sep 2018, 01:31
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A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

67% (01:21) correct 33% (01:14) wrong based on 6 sessions

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Both circles in the figure above have the same center, and the difference between their radii is 6. What is the outer circle’s radius?



(1) The outer circle’s area is 9 times the inner circle’s area.

(2) The inner circle’s circumference is \(\frac{1}{3}\) the outer circle’s circumference.

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Re M70-35  [#permalink]

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New post 04 Sep 2018, 01:31
Official Solution:


We’ll go for LOGICAL because that is our first choice in Data Sufficiency.

We have the gap between the radii but no other numbers; the outer circle’s radius is 6 more than inner circle’s radius. So, if we can calculate one, we’d know the other.

(1) Using the ratio between areas we can calculate the ratio between the radii (areas \(x^2:y^2\) --> radii \(x:y\)). With the ratio between the different radii we can express the small radii as a fraction of the large one, and together with the difference between them we can build an equation with one variable – sufficient! (B), (C) and (E) are eliminated.

(2) Again, using the given information, we can calculate the ratio between the radii. Now, just as in (1), we can create an equation with one variable to get the result we need. Sufficient. (A) is eliminated.


Answer: D
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Re: M70-35  [#permalink]

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New post 04 Sep 2018, 11:25
1
Hi Bunuel, the answer should be D. Please check.
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Re: M70-35  [#permalink]

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New post 04 Sep 2018, 16:54
1
Bunuel wrote:
Official Solution:


We’ll go for LOGICAL because that is our first choice in Data Sufficiency.

We have the gap between the radii but no other numbers; the outer circle’s radius is 6 more than inner circle’s radius. So, if we can calculate one, we’d know the other.

(1) Using the ratio between areas we can calculate the ratio between the radii (areas \(x^2:y^2\) --> radii \(x:y\)). With the ratio between the different radii we can express the small radii as a fraction of the large one, and together with the difference between them we can build an equation with one variable – sufficient! (B), (C) and (E) are eliminated.

(2) Again, using the given information, we can calculate the ratio between the radii. Now, just as in (1), we can create an equation with one variable to get the result we need. Sufficient. (D) is eliminated.


Answer: A


Hey Bunuel

Pl check OA.

OE and OA doesn't match.

Thnx.

Posted from my mobile device
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Re: M70-35  [#permalink]

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New post 04 Sep 2018, 19:56
Harshgmat wrote:
Bunuel wrote:
Official Solution:


We’ll go for LOGICAL because that is our first choice in Data Sufficiency.

We have the gap between the radii but no other numbers; the outer circle’s radius is 6 more than inner circle’s radius. So, if we can calculate one, we’d know the other.

(1) Using the ratio between areas we can calculate the ratio between the radii (areas \(x^2:y^2\) --> radii \(x:y\)). With the ratio between the different radii we can express the small radii as a fraction of the large one, and together with the difference between them we can build an equation with one variable – sufficient! (B), (C) and (E) are eliminated.

(2) Again, using the given information, we can calculate the ratio between the radii. Now, just as in (1), we can create an equation with one variable to get the result we need. Sufficient. (D) is eliminated.


Answer: A


Hey Bunuel

Pl check OA.

OE and OA doesn't match.

Thnx.

Posted from my mobile device

_____________________
Edited the OA. Thank you.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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.


What are GMAT Club Tests?
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Re: M70-35   [#permalink] 04 Sep 2018, 19:56
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