It takes 3 workers a total of 15 hours to build a giant machine with each worker working at the same rate. If 5 workers start to build the machine at 11:00 AM, and one extra worker per hour is added beginning at 1:00 PM, at what time will the machine be complete?  Choose the correct choice from the following options:  A) 4:30  B) 4:45  C) 5:00  D) 5:15  E) 5:30
3 workers build 1/15 of a machine in one hour.   1 worker builds 1/45 of a machine in one hour.   In the first 2 hours, 5 workers build 5*(1/45)*2=10/45 of a machine.   From 1:00 to 2:00, 6 workers build another 6/45. The total is 16/45.   From 2:00 to 3:00, 7 workers build another 7/45. The total is 23/45.   From 3:00 to 4:00, 8 workers build another 8/45. The total is 31/45.   From 4:00 to 5:00, 9 workers build another 9/45. The total is 40/45.   To build another 5/45, 10 workers need (5/10)*60 minutes which is 30 minutes.   The machine is complete at 5:30.   The answer is 5:30.
<result>E</result>
It takes 3 workers a total of 15 hours to build a giant machine with each worker working at the same rate. If 5 workers start to build the machine at 11:00 AM, and one extra worker per hour is added beginning at 1:00 PM, at what time will the machine be complete?