Barry runs an ice-cream shop and has 5 identical ice-cream-bar making machines,which he usually starts running at 7:00am so he would finish making all ice-creambars for the day at 9:00am. However, due to a power glitch at 7:18am, two of the ice-cream machines stopped working, though thankfully nothing turned bad.The power came back on at 7:25am (no ice-cream was made between 7:18am and 7:25am), and Barry still needs to make the exact same number of ice-creams, as the delivery truck is still coming to pick up the ice-cream bars. He must now find out the time when the machines would finish making all ice-cream bars for the day. Can you help him? Please answer in the format XX:YY, where XX is the hour, and YY isthe minute.

Guest Jan 10, 2021

#1**+1 **

Each machine completes 1/10 of the total work in 1 hour

3 work the whole 2 hours....so....they complete 2(1/10)*3 = 6/10 of the work during this time

The other two work one whole hour (between 8 and 9) without stopping so they complete another 1 (1/10) * 2 = 2/10 of the work during this time

So......we have accounted for 8/10 of the work

Between 7 and 8 the other two machines complete (53/60) * 2 (1/10) = 53/300 more of the work

So....the five machines complete 8/10 + 53/300 = 293/300 of the work in two hours

So....the five must complete 7/300 of the remaining work after 9 AM

Note that each minute.....one machine completes (1/10) (1/60) = 1/600 of the work

So..... each minute the 5 machines complete 5/600 = 1/120 of the work

So....the number of additional minutes they must work to complete the job is

Work remaining / portion of work done each minute =

(7/300) /( 1/120) = (7/300) (120) = 14/5 = 2.8 minutes = 2 min 48 sec

So....the time for completion is 9 AM + 2min 48 sec = 9:02:48

CPhill Jan 10, 2021