Question 36478
If Marvin can shovel it in 30 minutes, then in 1 minute he can shovel 1/20th of the driveway.   


If Nina can shovel it in 45 minutes, then in 1 minute she can shovel 1/45th of the driveway. 


Let x = number of minutes it will take them to shovel it off together.
Then in 1 minute, working together they can shovel 1/xth of the driveway.


This means that {{{ (1/20)+ (1/45)= 1/x}}}


The LCD for this equation is 180x, so multiply both sides of the equation by 180x.
{{{180x*(1/20)+ 180x*(1/45)= 180x*(1/x)}}}

{{{9x +4x = 180}}}

{{{13x = 180}}}


Divide both sides by 13:
{{{x = 180/13}}} minutes or approximately 13.84 minutes.


R^2 at SCC