Question 311386
Add their rates of working to get their
rate working together
Melanie's rate:
(1 barn painted)/(x days)
Melissa's rate:
(1 barn painted)/(2x days)
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Let the fraction of the barn they paint working 
together for 1 day = {{{y}}}
Their rate working together:
(y part of a barn painted)/(1 day)
{{{1/x + 1/(2x) = y/1}}}
{{{1/x + 1/(2x)}}} is the fraction of the barn painted
working together
{{{x = 5}}}
{{{1/5 + 1/10 = 3/10}}}
The paint 3/10 of the barn in 1 day