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?
a.) 120
b.) 40
c.) 24
d.) 20

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