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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

Practice Questions
Question: 53
Page: 159
Difficulty: 600


GMAT Club is introducing a new project: The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

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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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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

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Re: The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 10 Sep 2014, 18:08
Bunuel wrote:
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

Practice Questions
Question: 53
Page: 159
Difficulty: 600


GMAT Club is introducing a new project: The Official Guide for GMAT® Review, 13th Edition - Quantitative Questions Project

Each week we'll be posting several questions from The Official Guide for GMAT® Review, 13th Edition and then after couple of days we'll provide Official Answer (OA) to them along with a slution.

We'll be glad if you participate in development of this project:
1. Please provide your solutions to the questions;
2. Please vote for the best solutions by pressing Kudos button;
3. Please vote for the questions themselves by pressing Kudos button;
4. Please share your views on difficulty level of the questions, so that we have most precise evaluation.

Thank you!




10+30+50 = 90

90/3=30.

so mean of 20+40+x should be 25...

25*3=75(total),

60+x=75

x=15.
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The average (arithmetic mean) of 10, 30, and 50 is 5 more [#permalink] New post 10 Sep 2014, 21:54
Bunuel wrote:
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


Algebraic Method (Forming single equation for result)

\frac{10 + 30 + 50}{3} = \frac{20 + 40 + x}{3} + 5

x = 15

Shortcut (By observation) Method

10, 30, 50 are equally spaced; so average = 30

For the other set, required average would be 30 - 5 = 25

It means total = 75

Required number = 75 - (20+40) = 15
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The average (arithmetic mean) of 10, 30, and 50 is 5 more   [#permalink] 10 Sep 2014, 21:54
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