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John has 10 pairs of matched socks. If he loses 7 individual

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John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 11 Sep 2012, 04:41
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The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

John has 10 pairs of matched socks. If he loses 7 individual socks, what is the greatest number of pairs of matched socks he can have left?

(A) 7
(B) 6
(C) 5
(D) 4
(E) 3

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Question: 39
Page: 157
Difficulty: 600


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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 11 Sep 2012, 04:42
SOLUTION

John has 10 pairs of matched socks. If he loses 7 individual socks, what is the greatest number of pairs of matched socks he can have left?

(A) 7
(B) 6
(C) 5
(D) 4
(E) 3

General rule for such kind of problems:
to maximize one quantity, minimize the others;
to minimize one quantity, maximize the others.

The lowest number of pairs we can make from 7 individual socks is 3 pairs and one sock from a fourth pair. Hence, the greatest number of pairs of matched socks John can have left is 10 - 4 = 6.

Answer: B.
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RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

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. NEW!!!

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. NEW!!!


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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 11 Sep 2012, 09:28
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Since question is asking the Greatest number of pairs left after John loses 7 socks, it is better to count the socks in pairs.

In total 7 socks are lost, which can be counted as 3 pairs of socks (3x2) + 1 single socks. So in total 4 pairs are lost as 1 single sock can not be counted in a pair.

So, 10 - 4 = 6 pairs of socks.

B
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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 12 Sep 2012, 12:32
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John has 10 pairs of matched socks. If he loses 7 individual socks, what is the greatest number of pairs of matched socks he can have left?
(A) 7
(B) 6
(C) 5
(D) 4
(E) 3

Because we have to maximize the pair of matched socks, we will remove 3 pairs(6 socks) out of 10 pairs & 1 sock from the 4th pair.
Thus the no of matching socks pair remaining = 10 -4 = 6
Answer B

If we were asked minimum no of pairs of matched socks, we would have removed all the 7 socks from 7 different pairs out of 10 pairs.
Thus the no of matching socks pair remaining = 10 -7 = 3
Answer E

Hope it helps
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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 14 Sep 2012, 05:50
SOLUTION

John has 10 pairs of matched socks. If he loses 7 individual socks, what is the greatest number of pairs of matched socks he can have left?

(A) 7
(B) 6
(C) 5
(D) 4
(E) 3

General rule for such kind of problems:
to maximize one quantity, minimize the others;
to minimize one quantity, maximize the others.

The lowest number of pairs we can make from 7 individual socks is 3 pairs and one sock from a fourth pair. Hence, the greatest number of pairs of matched socks John can have left is 10 - 4 = 6.

Answer: B.

Kudos points given to everyone with correct solution. Let me know if I missed someone.
_________________

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

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. NEW!!!

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. NEW!!!


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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 17 Sep 2012, 10:46
I'm thinking that if he has 10 pairs, that is 20 socks. If he loses 7 individual socks, then the greatest number of socks he could have left is:

20-7= 13 -> 6 pairs, since 13/2 is not an integer.

Hence, the answer is B.
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Re: John has 10 pairs of matched socks. If he loses 7 individual [#permalink] New post 26 Nov 2012, 14:01
Hi there
This might sound silly but when I read this question I initially drew out aa bb cc etc as his socks and crossed out one letter of each 7 pairs which left me with 3 pairs left, could someone explain how clearly this is a wrong approach? How do I know that his socks are all the same. Thank u
Re: John has 10 pairs of matched socks. If he loses 7 individual   [#permalink] 26 Nov 2012, 14:01
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