akpareek wrote:Each of the 30 boxes in a certain shipment weighs either 10 pounds or 20 pounds, and
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
This is a great question for plugging in the answer choices, which represent the number of 20-pound boxes that need to be removed.
Current total weight = 30*18 = 540.
Answer choice C: 10 20-pound boxes removed.
New total weight = 540 - 10*20 = 340.
New number of boxes = 30-10 = 20.
New average = 340/20 = 17.
The average is too high, so we need to remove more boxes.
Eliminate A, B and C.
Answer choice D: 20 20-pound boxes removed.
New total weight = 540 - 20*20 = 140.
New number of boxes = 30-20 = 10.
New average = 140/10 = 14. Success!
The correct answer is
D.
Last edited by
GMATGuruNY on Wed Sep 28, 2011 4:02 am, edited 2 times in total.
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