Amber can paint a room in 20 hours. Christy can paint the same room in 16 hours. How long does it take for both amber and christy to paint the room if they are working together?

Answer: it will take them 8.89 hours

Step-by-step explanation:

Amber can paint a room in 20 hours. This means that Amber's working rate per hour is 1/20

Christy can paint the same room in 16 hours. This means that Christy's working rate per hour is 1/16

If they work together, they would be working simultaneously and their unit rates is additive. This means that their combined rate would be

1/20 + 1/16

Assuming it takes t hours for both of them to paint the room working together. It means that their combined working rate per hour is 1/t. Therefore

1/20 + 1/16 = 1/t

(16 + 20/320 = 1/t

36/320 = 1/t

t = 320/36

t = 8.89 hours