Eight machines, each working at the same constant rate, together can complete a certain job in 20 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 16 days?  Options:
A) 4  B) 6  C) 8  D) 10  E) 2
Rate of one machine = 1 job / (20*8) days   let X = number of machines needed to complete the job in 16 days   1/(8*20) * 16 * X = 1 job   X = 10   10-8= 
<gadget id="calculator">10-8</gadget>
<output>2</output>
2   ANSW2R: 2
<result>E</result>
Eight machines, each working at the same constant rate, together can complete a certain job in 20 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 16 days?