Twenty identical machines, running continuously at the same constant rate, take 14 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?	Choose the most appropriate option:  A) 8  B) 9  C) 12  D) 14  E) 16
From the question you know that 20R = 1/14. The question asks you (partially) to make the rate from 1/14 to 1/10 (drop from 14 day to 10). So the only thing that you need to do is to find the magic number than can convert 1/14 to 1/10.   So 1/14 * x = 1/10 (1 equation with one unknown). So by solving this you get x = 14/10 or 7/5. Thats it then! Take the magic number 7/5 and multiply BOTH sides of the original equation and you have:   20*(7/5)*R = (7/5) * 1/14   4 * 7 * R = 1/10, Hence 28R = 1/10, therefore 8 more machines!   8
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Twenty identical machines, running continuously at the same constant rate, take 14 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?