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At a certain stationery shop, the price of a pencil is 20 cents and th

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V
Joined: 02 Sep 2009
Posts: 51121
At a certain stationery shop, the price of a pencil is 20 cents and th  [#permalink]

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New post 25 Sep 2018, 03:56
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

65% (02:34) correct 35% (02:22) wrong based on 55 sessions

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At a certain stationery shop, the price of a pencil is 20 cents and the price of an eraser is 30 cents. A boy buys a total of 20 pencils and erasers from the shop, and the average (arithmetic mean) price of the 20 pieces comes to 28 cents. How many erasers must the boy return so that the average price of the pieces that he buys is 26 cents?

(A) 2
(B) 4
(C) 6
(D) 8
(E) 10

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S
Joined: 23 Nov 2017
Posts: 107
Location: Singapore
Concentration: Strategy, Other
GMAT 1: 660 Q49 V33
Re: At a certain stationery shop, the price of a pencil is 20 cents and th  [#permalink]

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New post 25 Sep 2018, 23:38
3
I did this by weighted averages.
Using allegation method, I get the ratio of pencils and erasers as 1:4

20 30
28
2 8 =2 : 8 = 1:4;
Splitting the total number of items in the above ratio, i know we have 4 pencils and 16 erasers.

Calculating weighted average for the average again, I get the new ratio as 2:3
20 30
26
4 6 = 4:6 = 2:3

Keeping the number of pencils as 4, i get the number of erasers as 6.
Subtracting 6 from 16, i get 10, which is the correct answer.

Help me with a kudo!
Senior Manager
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Joined: 02 Apr 2014
Posts: 474
GMAT 1: 700 Q50 V34
At a certain stationery shop, the price of a pencil is 20 cents and th  [#permalink]

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New post 23 Oct 2018, 22:40
1
1
Let E be number of erasers to be returned
so (28 * 20) - 30E = (20-E) * 26
560 - 30E = 520 - 26E
solving we get, E = 10 => Option (E)
GMAT Club Bot
At a certain stationery shop, the price of a pencil is 20 cents and th &nbs [#permalink] 23 Oct 2018, 22:40
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