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The average (arithmetic mean) of 10, 30, and 50 is 5 more

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The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 01 Oct 2012, 04:05
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The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and

(A) 15
(B) 25
(C) 35
(D) 45
(E) 55

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Question: 53
Page: 159
Difficulty: 600


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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 01 Oct 2012, 04:05
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SOLUTION

The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and

(A) 15
(B) 25
(C) 35
(D) 45
(E) 55

The average of 10, 30, and 50 is \frac{10+30+50}{3}=30.

The average of 20, 40 and x must be 30-5=25, so the sum of these 3 numbers must be 3*25=75 --> 20+40+x=75 --> x=15.

Answer: A.

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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 01 Oct 2012, 04:29
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The average of 10 30 50 is \frac{A = 10+30+50}{3} = 30
The second Average must be 5 less : 25. Using common sense or back solve we can obtain the solution.

Starting with A because we need a small value in the difference.

So,\frac{A = 20+40+15}{3} = 25

A is the answer

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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 01 Oct 2012, 18:47
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The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and
(A) 15
(B) 25
(C) 35
(D) 45
(E) 55

Average of 10,30,50 = 30
Average of 20,40 & x = 25
so 60 + x = 75----> x = 15
Answer A

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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 03 Oct 2012, 23:47
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Answer is A (15)

Since 10, 30 and 50 are numbers in equally spaced sets, average is 30

Now 30 is 5 greater than 25 ....Thus average of 20, 40 and (x) is 25 ......This implies, sum of 3 numbers should be 75 to make the average = 25

Thus, answer is 15 = 75 - 20 - 40
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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 04 Oct 2012, 13:05
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SOLUTION

The average (arithmetic mean) of 10, 30, and 50 is 5 more than the average of 20, 40, and

(A) 15
(B) 25
(C) 35
(D) 45
(E) 55

The average of 10, 30, and 50 is \frac{10+30+50}{3}=30.

The average of 20, 40 and x must be 30-5=25, so the sum of these 3 numbers must be 3*25=75 --> 20+40+x=75 --> x=15.

Answer: A.

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

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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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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more   [#permalink] 04 Oct 2012, 13:05
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