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# Average Price of fruit

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Retired Moderator
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Joined: 18 Jun 2009
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Concentration: Strategy, General Management
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Kudos [?]: 1075 [0], given: 157

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26 May 2010, 07:26
00:00

Difficulty:

(N/A)

Question Stats:

100% (03:22) correct 0% (00:00) wrong based on 4 sessions

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At a certain food stand, the price of each apple is $0.4 and the price of each orange is$0.6. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is $0.56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is$0.52?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5

Kindly share your working & also mention the time in which you have solved the question.
_________________
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Joined: 05 Mar 2008
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Kudos [?]: 277 [0], given: 31

Re: Average Price of fruit [#permalink]

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26 May 2010, 08:14
Hussain15 wrote:
At a certain food stand, the price of each apple is $0.4 and the price of each orange is$0.6. Mary selects a total of 10 apples and oranges from the food stand, and the average (arithmetic mean) price of the 10 pieces of fruit is $0.56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is$0.52?
(A) 1
(B) 2
(C) 3
(D) 4
(E) 5

Kindly share your working & also mention the time in which you have solved the question.

I know there is a fast way but I try to solve all these problems the same way
I use the letter "O" for oranges so it's not a zero after the .6

(.4A + .6O)/10 = .56 and A + O = 10
.4A + .6O = 5.6

Now subtract the above equation from A + O = 10
.4A + .6O = 5.6
-.4A - .4O = -4
.2O = 1.6
O = 8 so therefore A = 2

Now we try to find how many to take away to get the average of .52

.4(2) + .6(8-x) / 10-x = .52
.8 + 4.8 - .6x = 5.2 - .52x
5.6 - 5.2 = .6x - .52x
.04 = .08x
x = 5
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Joined: 04 May 2010
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Re: Average Price of fruit [#permalink]

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27 May 2010, 11:40
The initial average can be expressed as:

$$\frac{0.6x + 0.4(10-x)}{10} = 0.56$$, where x is the number of oranges.

$$4 + 0.2x = 5.6$$

$$x = 8$$

i.e. There were 2 apples and 8 oranges.

Now she puts back y oranges. The new average is:

$$\frac{0.6*(8-y) + 0.4*2}{10-y} = 0.52$$

$$5.6 - 0.6y = 5.2 - 0.52y$$

$$0.08y = 0.4$$

$$y = 5$$

So she puts back 5 oranges.
Pick E.

Takes about 1:15 to 1:30 to do this.
Re: Average Price of fruit   [#permalink] 27 May 2010, 11:40
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