GWD 03-28

[schung0529]

Q28:
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


The answer is D....拜託囉!

[yuang]

你可以設10 pounds 的箱子 X 個 , 20 pounds 的箱子 30-X 個, 平均18 pounds
可列算式: 10X + 20(30-X) = 30*18 解得 X=6

又 10 pounds 的箱子有6個, 20 pounds 的箱子有Y個時, 會讓平均變為14pounds

則 6*10 + Y*20 =14 (6+Y) 得Y=4 24-4=20 Ans:D

[little prince]