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Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?

 Jun 23, 2022
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1 / R  + 1 / S + 1 / T =1 / 4

 

1 / S  +  1 / T ==1 / 5

 

1 / R  +  1 / 5 ==1 / 4, solve R

 

R == 20 hours to finish the job working alone

 Jun 23, 2022

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