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Ariel, Bianca, and Camila are spray painting. Ariel could do it all by herself in $12$ hours, and Bianca could do it all by herself in $10$ hours. Ariel and Bianca work together for $3$ hours, then Camila joins in. The job finishes in another $2$ hours. How many hours would it take for Camila to do all the spray painting by herself?

 
 Nov 20, 2021
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Find the time for A and B together:

 

1 / (1 / A  + 1/B)  = T

    T = 60/11 = 5.55

 

they work for 3 hours ....this leaves   (4.55 - 3) / 5,55   job left = 0.4499625031247395967

Now all three work together and take two hours to complete the fraction of a job that is left:

 

.4499 /  ( 1/12 + 1/10 + 1/c)  =  2

c = 24 hours

 
 Nov 20, 2021

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