Three machines, each working at the same constant rate, together can complete a certain job in 18 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 9 days?
Options:
A) 3 B) 5 C) 7 D) 9 E) 8
Rate of one machine = 1 job / (18*3) days   let X = number of machines needed to complete the job in 9 days   1/(3*18) * 9 * X = 1 job   X = 6   6-3= 
<gadget id="calculator">6-3</gadget>
<output>3</output>
3   3NSWER: 3
<result>A</result>
Three machines, each working at the same constant rate, together can complete a certain job in 18 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 9 days?