請教一題

hiphoper

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

Answer:D

這題是不是不太對??

jikuren

答案是D
思路：设移走B个箱子(每个重20）后，总重量为540-20B，箱子剩下30-B:
(540-20B)/(30-B)=14
B=20

wentaow2008

  这题好像是gwd里的，算了好久~~~~~D应该是正解吧