Six machines at a certain factory operate at the same constant rate. If five of these machines, operating simultaneously, take 36 hours to fill a certain production order, how many fewer hours does it take all six machines, operating simultaneously, to fill the same production order?  Options.
A) 6  B) 8  C) 10  D) 12  E) 15
The total work is 5*36= 
<gadget id="calculator">5*36</gadget>
<output>180</output>
180 machine hours   The time required for six machines is  180/6= 
<gadget id="calculator"> 180/6</gadget>
<output>30</output>
30 hours, thus 6 fewer hours.   The answer is 6.
<result>A</result>
Six machines at a certain factory operate at the same constant rate. If five of these machines, operating simultaneously, take 36 hours to fill a certain production order, how many fewer hours does it take all six machines, operating simultaneously, to fill the same production order?