Question 945014
Phyllis rakes 1 lawn in 50 min=1 lawn/50 min=1/50 lawn/min
I rake 1 lawn in 40 min=1 lawn/40 min=1/40 lawn/min
In the first five minutes, Phyllis rakes 5min(1/50 lawn/min)=5/50 lawn=1/10 lawn
Together Phyllis and I rake at a rate of 1/50 lawn/min + 1/40 lawn/min=
(Find common denominator)   4/4(1/50)lawn/min + 5/5(1/40) lawn/min=
4/200 lawn/min + 5/200 lawn/min= 9/200 lawn/min together
Phyllis has raked 1/10 of the lawn leaving 9/10 to rake (convert to 200ths)
20/20(9/10)lawn=180/200 lawn left to rake 
together we rake 9/200 lawn/min so (180/200)/(9/200) min=20 minutes
ANSWER: It takes 20 additional minutes for both to finish the lawn.