Question 733515
1/12 + 1/15 + 1/20 = 1/t


5/60 + 4/60 + 3/60 = 1/t


(5+4+3)/60 = 1/t


12/60 = 1/t


1/5 = 1/t


1*t = 5*1


t = 5


So if all machines are working together (with no one machine hindering the other), then they will fill the quota in 5 hours.