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 8,000 have been vaccinated against both, how many have been vaccinated only against rubella?	Choose the correct choice from the following options: A) 2,5000 B) 7,500 C) 10,000 D) 15,000 E) 16,000
Use a single variable as far as possible.   Number vaccinated only against mumps = x   Number vaccinated against both = 2x = 8000 (so x = 4000)   Then, number vaccinated against mumps (including both) = x + 2x = 3x   Number vaccinated against rubella = 2*3= 
<gadget id="calculator">2*3</gadget>
<output>6</output>
6x   Then, number vaccinated against only rubella= 6x - 2x = 4x 6  - 2= 
<gadget id="calculator">6  - 2</gadget>
<output>4</output>
4x= 4*4000 = 16,000   Answer (16,000)
<result>E</result>
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 8,000 have been vaccinated against both, how many have been vaccinated only against rubella?