请问这道数学题是什么意思？

qiongyue0312

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

qiongyue0312

我没有理解这题的意思。不知道是不是这样理解：

接种R的是接种M的两倍,然后两个都接种的是只接种M的两倍。。完全混乱了。。

uustar

这题你画个图就出来了。设只种m的为x，both r and m就是2x，那么种r的一共是2倍的x+2x，就是6x，只种r的就是4x。题目给了两个都种的是5000，那么只种r的就是10000。

qiongyue0312

谢谢uustar!

我懂了~

The number who have been vaccinated against both is twice the number who have been vaccinated only against mumps

我漏掉了only,算了半天怪不得不对！！

我漏掉了only,算了半天怪不得不对！！

honey67

为什么我算出来R还是5000呢？
根据前一句推出：R=2M
后面一句推出： B（both)=2M=5000
M=2500
R=5000

我的思路哪里出错了？请同学们帮我指正一下。
谢谢。