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Some PS questions- Need explanation

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Some PS questions- Need explanation [#permalink]

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New post 17 Aug 2010, 05:18
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A
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D
E

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Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

1.At a certain food stand, the price of each apple is ¢ 40 and the price of each orange is ¢60. 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 ¢ 56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is ¢52?
A. 1
B. 2
C. 3
D. 4
E. 5

OA E
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Re: Some PS questions- Need explanation [#permalink]

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New post 17 Aug 2010, 08:31
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udaymathapati wrote:
Need help in explanation of following problems. Need to know how quickly we can solve such problems to save time.

1.At a certain food stand, the price of each apple is ¢ 40 and the price of each orange is ¢60. 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 ¢ 56. How many oranges must Mary put back so that the average price of the pieces of fruit that she keeps is ¢52?
A. 1
B. 2
C. 3
D. 4
E. 5

OA E



Answer: 5

Original Cost--- Apples : Oranges
56 * 10 --- 2 : 8

Gives away n number of oranges and the mean becomes 52.
Hence
52*(10 - n) --- 2 : (8 -n)

Setting up the equation for the total value.

52 * (10 - n) = (2 * 40) + ((8 - n)* 60)

520 - 52 n = 80 + 480 - 60 n

560 - 520 = 8 n

8n = 40

n = 5.

Answer: E
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Re: Some PS questions- Need explanation [#permalink]

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New post 17 Aug 2010, 15:56
oranges : o
apples : a
given :
o+a = 10--(1)
(40a+60o) /10= 56 ----(2)

by solving (1) and (2) we can get

o = 8
a = 2
we need to get avg = 52 cents
s = number of oranges to be taken out
40a+60o / (10 - s) = 52

40 * 2 + 60 (8 -s) = 520 - 52s
560 - 60s = 520 -52s
40 = 8s
s = 5 answer
Re: Some PS questions- Need explanation   [#permalink] 17 Aug 2010, 15:56
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Some PS questions- Need explanation

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