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M23-19

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Joined: 02 Sep 2009
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M23-19  [#permalink]

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New post 16 Sep 2014, 01:19
00:00
A
B
C
D
E

Difficulty:

  25% (medium)

Question Stats:

82% (01:19) correct 18% (02:08) wrong based on 168 sessions

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Mike has to take five tests containing 80 questions each. If after completing four tests, Mike has an average of 80 percent of correct answers, what is the least number of questions Mike needs to get right in the fifth test to bring his average to 82% ?

A. 70
B. 72
C. 75
D. 78
E. 80

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Re M23-19  [#permalink]

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New post 16 Sep 2014, 01:19
Official Solution:

Mike has to take five tests containing 80 questions each. If after completing four tests, Mike has an average of 80 percent of correct answers, what is the least number of questions Mike needs to get right in the fifth test to bring his average to 82% ?

A. 70
B. 72
C. 75
D. 78
E. 80


In order to answer the question, we need to know how many questions were answered correctly in the first four tests.

\(80*4=320\), \(320*80\%=256\)

Now we have to find out how many questions of all 400 questions from 5 tests need to be answered correctly so that the average of 82% is achieved:

\(400*82\%=328\)

Finding the difference between 328 and 256 we can answer the question of the problem:

\(328-256=72\)


Answer: B
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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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M23-19  [#permalink]

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New post 03 Jul 2017, 07:35
1
1
I guess this can be approached using the Alligation method as well. In case anyone interested, this is how I did it. Snapshot attached


From the Alligation we get

\(\frac{4}{1} = \frac{(x - 82)}{2}\)

\(8 = (x-82)\)

\(90 = x\)

Meaning mike has to get 90% questions right in his 5th attempt

=\((90/100) * 80 = 72\)


Final Answer : B

>> !!!

You do not have the required permissions to view the files attached to this post.


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Re: M23-19  [#permalink]

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New post 12 Mar 2018, 06:37
My approach was:

in previous 4 tests mike got 2% less in each. In the fifth test he should get 5 times 2% to increase the average % by 2.
80*80%=64
80*10%=8 Mikes current average score needs 8 points more to achieve 2% increase.

Does such approach make sense?
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Re: M23-19  [#permalink]

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New post 12 Mar 2018, 07:16
LevanKhukhunashvili wrote:
My approach was:

in previous 4 tests mike got 2% less in each. In the fifth test he should get 5 times 2% to increase the average % by 2.
80*80%=64
80*10%=8 Mikes current average score needs 8 points more to achieve 2% increase.

Does such approach make sense?

______________
Absolutely.
_________________

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.


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Re: M23-19 &nbs [#permalink] 12 Mar 2018, 07:16
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