It takes Rumi 15 minutes to inspect a machine and Sami needs 18 minutes to inspect a machine. They both start inspecting machines separately at 9:00 AM. At certain points of time, both of them will finish inspecting a machine at the same time. When will this occur for the first time?

LCM of 15 & 18 are 90Here 90 minutes = 1 hour 30 minutesSo, inspecting machine at the same time will be = 9:00 AM + 1 hour 30 minutes                                                                                                   = 10:30 AM (Ans)