Working at their respective constant rates, machine A makes 100 copies in 12 minutes and machine B makes 150 copies in 15 minutes. If these machines work simultaneously at their respective rates for 30 minutes, what is the total number of copies that they will produce? Choose the correct choice.
A) 250  B) 425  C) 550  D) 700  E) 750
Machine A can produce 100 *30/12= 
<gadget id="calculator">100 *30/12</gadget>
<output>250</output>
250 copies   And, Machine B can produce   150* 30/15= 
<gadget id="calculator">  150* 30/15</gadget>
<output>300</output>
300 Copies   Total producing 550 Copies.   550 is the answer
<result>C</result>
Working at their respective constant rates, machine A makes 100 copies in 12 minutes and machine B makes 150 copies in 15 minutes. If these machines work simultaneously at their respective rates for 30 minutes, what is the total number of copies that they will produce?