10 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?  Choices:  A) 2  B) 3  C) 4  D) 5  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* 10= 
<gadget id="calculator">3/2* 10</gadget>
<output>15</output>
15   So we need   15-10= 
<gadget id="calculator">  15-10</gadget>
<output>5</output>
5 more machines.   Answer : 5
<result>D</result>
10 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?