Algebra
posted by Laura on .
Word Problem:
Jack mows the lawn in 4 hours, mary mows the lawn in 5 hours. how long will it take them if they mowed the lawn together?
I have a hard time figuring out which formula to use to solve a problem in a word problem can anyone help and tell me how to set up the problem so I can do the math?

Hello Laura,
the method that i would recommend is this simple method (assuming that both of them mow the lawn at a constant speed):
Jack>4h can complete lawn
jack>1h can complete 1/4 lawn
Mary>5h can complete lawn
Mary>1h can complete 1/5 lawn
Together>1h can complete 1/4+1/5=9/20 lawn.
That means that in 1 hour they can complete 9/20 lawn. To figure out time just take 20/20 divide by 9/20, the answer is 2/2/9. Hope that helps ^_^. Of course don't forget to put it in hours! ^_^ 
The combined rate of lawn mowing is 9/20 lawn/hour. To mow one lawn therefore takes 20/9 hour, or 2 and 2/9 hours.
Deanna's answer was correct but the 2/2/9 at the end was mistyped. 
Hello Drwls,
sorry, but i don't understand what you mean by the 2/2/9 at the end was mistyped? Thank you for correcting my mistake if i had made one though! ^_^