[求助]gwd 3-14

qiuqiaomm

Q14:

Box W and Box V each contain several blue sticks and red sticks, and all of the red sticks have the same length. The length of each red stick is 18 inches less than the average length of the sticks in Box W and 6 inches greater than the average length of the sticks in Box V. What is the average (arithmetic mean) length, in inches, of the sticks in Box W minus the average length, in inches, of the sticks in Box V?

A. 3

B. 6

C. 12

D. 18

E. 24

这题我怎么觉得选不出答案。得出24这个答案是不是要默认两个盒子里红色的数量一样多、蓝色的数量也一样多？还是我在钻牛角尖了？盼回复！谢谢！

robert

不需要考虑数量。这题是个迷惑题。

假设red的长度是x，则W的average length是x+18，V的average length是x-6

所以W-V=x+18-(x-6)=24

qiuqiaomm

谢谢robert! 中秋快乐！

nikema

我觉得你可能没有仔细看这句话:

The length of each red stick is 18 inches less than the average length of the sticks in Box W and 6 inches greater than the average length of the sticks in Box V

可以假设每个red stick的length为 A 那么 the average length of the sticks in Box W 就为 A+18

the average length of the sticks in Box V 为 A-6

所以average ( B-A) 就是 (A+18) -(A-6)=24

qiuqiaomm

谢谢！我真是莫名其妙，竟然把the average length of the sticks in Box W and the average length of the sticks in Box V看成了 the average length of the (blue) sticks in Box W and the average length of the (blue) sticks in Box V。