GWD28-29

lengling

 

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

Why not B

Thank you.

qq6501215

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lengling

Thank you
My answer is 20(B-m)=18*30-14*30
So, B-m=6
So, answer is B
Where am I wrong?

yoyo9012

LZ 列两个方程就OK了
A+B=30 和10A+20B/30=18 算出A=6 B=24
然后设需移除X个B 得：10X6+20（24-X）/ 30-X=14 解得X=20