Question

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 5000 have been vaccinated against both, how many have been vaccinated only against rubella?

A. 2500
B. 7500
C. 10000
D. 15000
E. 17500

Answer 1

C. 10 000

Explanation:

If we called:

x = children who have been vacinated against rubella only

2x = children who have been vaccinated against mumps

y = children who have been vaccinated agains both

Children who have been vaccinated against mumps only = x - y

And we know that y = 2*(x-y)

=> 2y = 3x

y = 5000

There fore x = 7500

The number of children who have been vaccinated against rubella

= 2x - y = 2*7500 - 5000 = 15 000 - 5000 = 10 000