GWD-11-19 为啥这道题没人问 我觉得这道题最难

mandaran

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

channing76

设种rubella为X，mumps为Y，已知二者都种为5000，据条件X=Y2 ; 5000=2(Y--5000); so we can draw the conclusion from the (x-5000);