Question 227576
In words:
(Bert's rate of working) + (Ernie's rate of working) = (rate working together)
(1 lawn/5 hours) + (1 lawn/x hours) = 1 lawn/3 hours)
{{{1/5 + 1/x = 1/3}}}
Multiply both sides by {{{15x}}}
{{{3x + 15 = 5x}}}
{{{2x = 15}}}
{{{x = 7.5}}}
Ernie can rake the lawn alone in 7.5 hours
check:
{{{1/5 + 1/7.5 = 1/3}}}
{{{3/15 + 2/15 = 5/15}}}
{{{3 + 2 = 5}}}
{{{5 = 5}}}
OK