Guy can mow his entire lawn in 20 minutes; Guy's roommate Lazar needs 30 minutes to mow the entire lawn. If Guy starts mowing at 1 p.m., mows for five minutes and then Lazar starts to help with his own mower, at what time will they finish mowing the lawn?
In 5 minutes there will be only 3/4 of the lawn left to mow.
Guy can mow 3/4 in 15 min Lazar can mow 3/4 in 22.5 min
1/15 + 1/22.5 = 1/x solve for x = 9 mins to finish the lawn
1:00 pm + 5 min + 9 min = 1:14 PM