One copy machine can make 30 copies a minute, and a second copy machine makes 15 copies a minute. If the two copiers work together, how long would it take them to make 900 copies? Choose the correct choice from the following options
A) 15 minutes B) 20 minutes C) 25 minutes D) 30 minutes E) 35 minutes
Total work done by both machines in a minute = 30 + 15= 
<gadget id="calculator">30 + 15</gadget>
<output>45</output>
45 copies   Total number of copies required= 900   Time = 900/45= 
<gadget id="calculator">900/45</gadget>
<output>20</output>
20 mins   Answer 20 minutes
<result>B</result>
One copy machine can make 30 copies a minute, and a second copy machine makes 15 copies a minute. If the two copiers work together, how long would it take them to make 900 copies?