SOLUTION: Together, Mary and John can write a particular type of computer program in 15 hours. Alone, Mary can do the job 3 hours faster than John. Find the time that each person takes to w

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Together, Mary and John can write a particular type of computer program in 15 hours. Alone, Mary can do the job 3 hours faster than John. Find the time that each person takes to w      Log On


   

Question 878209: Together, Mary and John can write a particular type of computer program in 15 hours. Alone, Mary can
do the job 3 hours faster than John. Find the time that each person takes to write a computer program.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Add their rates of working
Together:
( 1 program ) / ( 15 hrs )
John alone:
( 1 program ) / ( t hrs )
Mary alone:
( 1 program ) / ( t - 3 )
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+1%2Ft+%2B+1%2F%28+t-3+%29+=+1%2F15+
Multiply both sides by +15%2At%2A%28+t-3+%29+
+15%2A%28+t-3+%29+%2B+15t+=+t%2A%28+t-3+%29+
+15t+-+45+%2B+15t+=+t%5E2+-+3t+
+t%5E2+-+33t+%2B+45+=+0+
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Solve for +t+ with quadratic formula
then find +t+ and +t+-+3+