Four machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the Job in 8 days?
Pick:  A) 2  B) 3  C) 4  D) 6  E) 8
Another solution which is faster is Since each machine works at a constant rate. The time needs to bought down from 12 to 8. So the new time is 2/3 of the original time. Thus to achieve this we need the rate to be 3/2 of original.   So 3/2* 4= 
<gadget id="calculator">3/2* 4</gadget>
<output>6</output>
6   So we need   6-4= 
<gadget id="calculator">  6-4</gadget>
<output>2</output>
2 more machines.   2nswer : 2
<result>A</result>
Four machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the Job in 8 days?