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# Each of the 30 boxes in a certain shipment with either 10

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Intern
Joined: 08 Nov 2008
Posts: 29
Each of the 30 boxes in a certain shipment with either 10 [#permalink]

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09 Nov 2008, 19:13
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Each of the 30 boxes in a certain shipment with either 10 pounds or 20 pounds, and the average (arithmetic mean) weight of the boxes in the shipment is 18 pounds. If the average weight of the boxes in the shipment is to be reduced to 14 pounds by removing some of the 20-pound boxes, how many 20-pound boxes must be removed?

A. 4
B. 6
C. 10
D. 20
E. 24
Intern
Joined: 07 Nov 2008
Posts: 32

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09 Nov 2008, 20:18
petercao wrote:
Each of the 30 boxes in a certain shipment with either 10 pounds or 20 pounds, and the average (arithmetic mean) weight of the boxes in the shipment is 18 pounds. If the average weight of the boxes in the shipment is to be reduced to 14 pounds by removing some of the 20-pound boxes, how many 20-pound boxes must be removed?

A. 4
B. 6
C. 10
D. 20
E. 24

(10x+20y)/(x+y)=18
x+y=30
x=6,y=24

(10*6+20z)/(6+z)=14
z=4

24-4=20

D
Manager
Joined: 08 Aug 2008
Posts: 229

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10 Nov 2008, 00:05
D.
echo the same explanation:

10x+20y=540==> 2z+y=54--(1)

x+y=30----(2)

x=6, y=24

60+ 20z=14(6+z)
=> z=4.

so 24-4=20 boxes were removed.
Manager
Joined: 14 Oct 2008
Posts: 160

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10 Nov 2008, 03:21
D with a different way of computing.

540 - 20x = 14(30 - x)
x = 20.
Re: boxes--28   [#permalink] 10 Nov 2008, 03:21
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# Each of the 30 boxes in a certain shipment with either 10

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