Five 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 10 days?
Answers.
A) 4	B) 6	C) 8	D) 5	E) 10
Rate of one machine = 1 job / (20*5) days   let X = number of machines needed to complete the job in 10 days   1/(5*20) * 10 * X = 1 job   X = 10   10-5= 
<gadget id="calculator">10-5</gadget>
<output>5</output>
5   ANSWER: 5
<result>D</result>
Five 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 10 days?