Alexander's copy store received an order for 4,320 copies. The store has 3 printers. If Alexander only uses one printer at a time, the first printer would complete the job in 8 hours, the second in 12 hours, and the third in 9 hours. How long would it take to process the order if all three printers were used at the same time?
+36916 1 job / combined rate = time required
1/ ( 1/8 + 1/12 + 1/9) = hours ( Note that 4320 is irrelevant)
