<PRE><B>Question 857258</B>
Jessica can type a manuscript in 8 hours.  Heather can type the same manuscript in 13 hours.  If they work together, how long will it take to process the manuscript?

Jessica can type a manuscript in 8 hours.

she can do 1/8 of the job in 1 hour

  Heather can type the same manuscript in 13 hours. 

he can do 1/13 of the job in 1 hour


Together they can do

1/8 + 1/13 of the job in 1 hour

(13+8)/13*8 of the job in 1 hour

21/104 

so they will take 104/21 hours to complete the job together

=4.95 hours
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