Jannette can repair a refrigerator in 60 minutes. Liza can repair a refrigerator 20 minutes faster. If they work together, how many minutes does it take them to repair the refrigerator

24 minutes. Assuming that 2 people who will repair a refrigerator equally fast will do it twice as fast when working together:
Jannete repairs 1/60 refrigerator per minute.
Lisa repairs 1/40 refrigerator per minute.
Togheter they repair 1/60+1/40= 1/60 + 1,5/60 = 2,5/60=5/120=1/24 refrigerator per minute
thus it will take them 24 minutes