I dont understand work problems, please help

Question

an example would be: Phyllis can rake our lawn in 50 minutes, and I can do in in 40. If she rakes by herself for 5 minutes, then I join her, how long will it take for us to rake the lawn?

Answer 1

50 minutes  - 1 ( whole lawn)

 

5 minutes  - ( lawn ) / 10 

 

 

or one tenth of the lawn

 

entire lawn - 45 mins

 

nine tenths of the lawn - 45 * (9/10) = 40.5 minutes

 

However the total time taken = 40.5 + 5 = 45.5 mins because Phyllis raked (1/10) of the lawn by herself in 5 minutes.

 

Ans : 45.5 minutes