Let Dan's pace be x

let Julio's pace be x-10

Total propotion:



Cross multiply:





Multiply the whole equation by 12 to remove the fraction:



Simplfy:



Put it into  form:



Use the quadratic formula:

 

In which a=1, b=-34, c=120

 

Remove the negative sign:





x=30

30-10=20

Hence, Julio can mow the lawn is 20 minuites and Dan can mow the lawn is 30 minutes when working alone.

Paul. 

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