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If x, y, and z are numbers, is z = 18 ?

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If x, y, and z are numbers, is z = 18 ? [#permalink] New post 04 Feb 2014, 00:52
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C
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Difficulty:

  5% (low)

Question Stats:

88% (01:37) correct 12% (00:38) wrong based on 90 sessions
The Official Guide For GMAT® Quantitative Review, 2ND Edition

If x, y, and z are numbers, is z = 18 ?

(1) The average (arithmetic mean) of x, y, and z is 6.
(2) x = -y

Data Sufficiency
Question: 74
Category: Arithmetic Statistics
Page: 158
Difficulty: 600


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Expert Post
Math Expert
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Joined: 02 Sep 2009
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Kudos [?]: 28713 [0], given: 2820

Re: If x, y, and z are numbers, is z = 18 ? [#permalink] New post 04 Feb 2014, 00:52
Expert's post
SOLUTION

If x, y, and z are numbers, is z = 18 ?

(1) The average (arithmetic mean) of x, y, and z is 6 --> x + y + z = 6*3 = 18. We cannot say whether z = 18. Not sufficient.

(2) x = -y --> x + y = 0. Clearly insufficient.

(1)+(2) x + y + z = 18 --> 0 + z = 18 --> z = 18. Sufficient.

Answer: C.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

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; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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.


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Kudos [?]: 54 [0], given: 29

Re: If x, y, and z are numbers, is z = 18 ? [#permalink] New post 04 Feb 2014, 03:38
Ans. C

From S1: x+y+z=18.Not sufficient

From S2: x+y=0.Not sufficent to determine z

Combining the two we get z=18 definitely.Both are together sufficient.
1 KUDOS received
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Kudos [?]: 3 [1] , given: 17

Re: If x, y, and z are numbers, is z = 18 ? [#permalink] New post 04 Feb 2014, 04:37
1
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My answer is also C (explanation is already provided, so not doing honours)
Expert Post
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Joined: 02 Sep 2009
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Kudos [?]: 28713 [0], given: 2820

Re: If x, y, and z are numbers, is z = 18 ? [#permalink] New post 08 Feb 2014, 04:38
Expert's post
SOLUTION

If x, y, and z are numbers, is z = 18 ?

(1) The average (arithmetic mean) of x, y, and z is 6 --> x + y + z = 6*3 = 18. We cannot say whether z = 18. Not sufficient.

(2) x = -y --> x + y = 0. Clearly insufficient.

(1)+(2) x + y + z = 18 --> 0 + z = 18 --> z = 18. Sufficient.

Answer: C.
_________________

NEW TO MATH FORUM? PLEASE READ THIS: ALL YOU NEED FOR QUANT!!!

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; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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?
25 extra-hard Quant Tests

Get the best GMAT Prep Resources with GMAT Club Premium Membership

Re: If x, y, and z are numbers, is z = 18 ?   [#permalink] 08 Feb 2014, 04:38
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