Question 1005044
Mary can wash her car in 40 minutes. Tina can wash the car in 25 minutes. 
How long will it take to wash the car if both girls work together on the task?
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Mary makes {{{1/40}}} of the entire job per minute.


Tina makes  {{{1/25}}}  of the entire job per minute.


Both of them make  {{{1/40}}} + {{{1/25}}}  of the entire job per minute working together.


It is equal to  {{{5/200}}} + {{{8/200}}} = {{{13/200}}}  of the entire job per minute.


Hence,  they need  {{{200/13}}}  minutes to complete the job.


It is  {{{15}}}{{{5/13}}}  minutes.