SOLUTION: Michael can mow the lawn in half an hour, and Alex can mow it in three quarters of an hour. Suppose Michael spends 20 minutes on the job, and then Alex finishes it. How long does

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Michael can mow the lawn in half an hour, and Alex can mow it in three quarters of an hour. Suppose Michael spends 20 minutes on the job, and then Alex finishes it. How long does      Log On


   

Question 933424: Michael can mow the lawn in half an hour, and Alex can mow it in three quarters of an hour. Suppose Michael spends 20 minutes on the job, and then Alex finishes it. How long does Alex have to work?
Answer by josgarithmetic(39629) About Me  (Show Source):
You can put this solution on YOUR website!
RT=J, and if the job is split into separate parts then RT terms are added to make the whole or total amount of jobs.

R for rate is used in units of JOBS per HOUR.

Michael_Alone+Alex_Alone, making ONE whole job.
%281%2F%281%2F2%29%29%281%2F3%29%2B%281%2F%283%2F4%29%29%2At=1, assigning t as the time in HOURS for Alex to finish. Solve for t.

2%2F3%2B%284%2F3%29t=1
2%2B4t=3
4t=1
highlight%28t=1%2F4%29
Fifteen minutes.