SOLUTION: Holly takes 50 minutes to mow the lawn. It takes erich an hour to mow the same lawn. One day Holly started mowing the lawn by herself and worked for 10 minutes. Then Erich joined h

Question 98384: Holly takes 50 minutes to mow the lawn. It takes erich an hour to mow the same lawn. One day Holly started mowing the lawn by herself and worked for 10 minutes. Then Erich joined her and they finished the lawn together. How long did it take them to finish mowing the lawn after Erich started to help?
Answer by edjones(8007) (Show Source): You can put this solution on YOUR website!
Holly can do 1/50 of the job per minute
Erich can do 1/60 of the job per minute
Holly works alone for 10 min. she does 10/50 or 1/5 of the job.
both together = 1/50+1/60=6/300+5/300=11/300 job per minute.
t=time in minutes
11t/300=4/5
t=4/5*(300/11)=21 9/11minutes
So the total time it takes is 21+10= 31 minutes and 49 seconds(9/11*60)
Ed
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