Q19:

In a certain region, the number of children who have been vaccinated against rubella is twice the number who have been vaccinated against mumps.  The number who have been vaccinated against both is twice the number who have been vaccinated only against mumps.  If 5,000 have been vaccinated against both, how many have been vaccinated only against rubella?

A.        2,500

B.         7,500

C.        10,000

D.        15,000

E.         17,500

我的答案是C。 不对吗？

不知道你怎么做出来的，我计算出来的就是15000 没什么特别的

题目的意思是：在某一特定区域，接种过风疹疫苗的孩子的数量是接种过腮腺炎疫苗的孩子的数量的两倍，而接种过风疹和腮腺炎疫苗的孩子的数量是仅仅接种过腮腺炎疫苗的孩子的数量的两倍，如果接种过风疹和腮腺炎疫苗的孩子的数量是5000，问接种过风疹的孩子的数量是多少？

首先 由于 “接种过风疹和腮腺炎疫苗的孩子的数量是5000“ && “接种过风疹和腮腺炎疫苗的孩子的数量是仅仅接种过腮腺炎疫苗的孩子的数量的两倍“ => “仅仅接种过腮腺炎疫苗的孩子的数量是2500“

其次，由于 接种过风疹和腮腺炎疫苗的孩子的数量 + 仅仅接种过腮腺炎疫苗的孩子的数量 = 所有接种过腮腺炎疫苗的孩子的数量

可以得到：所有接种过腮腺炎疫苗的孩子的数量 = 5000 + 2500 = 7500

最后，由于 “接种过风疹疫苗的孩子的数量是接种过腮腺炎疫苗的孩子的数量的两倍” && "所有接种过腮腺炎疫苗的孩子的数量 = 5000 + 2500 = 7500"  =>  "种过风疹的孩子的数量是7500*2 = 15000"

The correct answer is D, 15,000

正确答案无疑是D

这一期的GWD数学答案好像做的不太认真

可以看一下同一期前面那道圆心面积的题，同一道题之前出现过，但是这里答案也错了.

1.Vaccinated against rubella is twice the number who have been vaccinated against mumps. 
2.Vaccinated against both is twice the number who have been vaccinated only against mumps. 
3.5,000 have been vaccinated against both

r=rubella, m=mumps,ro=rubella only, mo=mumps only

Q: How many have been vaccinated only against rubella(ro)?

ro=r-rm
r=2m
m=mo+rm
rm=2mo
rm=5000

So,
mo=2500
m=mo+rm=2500+5000=7500
r=2m=2(7500)=15000
ro=r-rm=15000-5000=10000

C=10000吧?