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M06-33

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M06-33  [#permalink]

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New post 16 Sep 2014, 01:51
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A
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Difficulty:

  15% (low)

Question Stats:

89% (01:19) correct 11% (01:54) wrong based on 28 sessions

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A music store has 90 different CD's. If an average price is $12 per CD and 20 of the most expensive ones are $20 each, what is the average price of the remaining CD's?

A. 8.33
B. 8.75
C. 9.23
D. 9.71
E. 10.07

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Re M06-33  [#permalink]

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New post 16 Sep 2014, 01:51
Official Solution:

A music store has 90 different CD's. If an average price is $12 per CD and 20 of the most expensive ones are $20 each, what is the average price of the remaining CD's?

A. 8.33
B. 8.75
C. 9.23
D. 9.71
E. 10.07


The sum of the prices of all CD's is \(90 * $12 = $1,080\).

The sum of the prices of the most expensive CD's is $400. So, \($1,080 - $400 = $680\) is left for 70 remaining CD's. Thus the average price is \(\frac{$680}{70} = $9.71\)


Answer: D
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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: M06-33  [#permalink]

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New post 10 Jul 2018, 06:41
Hi chetan2u niks18 pushpitkc pikolo2510 Abhishek009

Is below approach (presumably of weighted average) valid:

[(20*20) + (x*70)] / 90 =12

Simplifying gives same result :-)
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M06-33  [#permalink]

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New post 10 Jul 2018, 06:45
first we need to find total sum then subtract the most expensive ones and divide the rest
12*90=1080-400(20*20)=680/70=9.7 (D)
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Re: M06-33  [#permalink]

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New post 10 Jul 2018, 07:25
adkikani wrote:
Hi chetan2u niks18 pushpitkc pikolo2510 Abhishek009

Is below approach (presumably of weighted average) valid:

[(20*20) + (x*70)] / 90 =12

Simplifying gives same result :-)


If you look closely, It is actually the same method as bunuel solved it.

Multiple by 90 on RHS and subtract 20*20 i.e.

x*70 = 90*12 - 20*20
x*70 = 1080 - 400
x*70 = 680
x = 680/70

x = 9.71
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Re: M06-33 &nbs [#permalink] 10 Jul 2018, 07:25
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