Question 319389
Add their rates working separately to get
theirs rates working together
In words:
(1 job/a's time) + (1 job/b's time) = 1 job/working together
{{{1/4 + 1/6  = 1/x}}}
multiply both sides by {{{12x}}}
{{{3x + 2x  = 12}}}
{{{5x = 12}}}
{{{x = 12/5}}}
Working together, they can do the job in 2.4 hrs