Ten identical machines, running continuously at the same constant rate, take 6 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by four days?
Pick.
A) 25  B) 20  C) 14  D) 9  E) 5
From the question you know that 10R = 1/6. The question asks you (partially) to make the rate from 1/6 to 1/2 (drop from 6 day to 2). So the only thing that you need to do is to find the magic number than can convert 1/6 to 1/2.   So 1/6 * x = 1/2 (1 equation with one unknown). So by solving this you get x = 6/2 or 3/1. Thats it then! Take the magic number 3/1 and multiply 20OTH sides of the original equation and you have:   10*(3/1)*R = (3/1) * 1/6   10 * 3 * R = 1/2, Hence 30R = 1/2, therefore 20 more machines!   20
<result>B</result>
Ten identical machines, running continuously at the same constant rate, take 6 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by four days?