Question 994156
Since they only talk about 15 dishes, I
will say: 15 dishes = 1 job
Dana's rate of washing is:
{{{ 1/15 }}} job/min
Dave's rate of washing is :
{{{ 1/25  }}} jobs/min

-----------------------
Let {{{ t }}} = minutes to wash 15 dishes
when they work together
{{{ 1/15 + 1/25 = 1/t }}}
Multiply both sides by {{{ 75t }}}
{{{ 5t + 3t = 75 }}}
{{{ 8t = 75 }}}
{{{ t = 9.375 }}} min
{{{ .375*60 = 22.5 }}}
It will take them 9 min 22.5 sec working together
-----------------
check:
{{{ 1/15 + 1/25 = 1/t }}}
{{{ 1/15 + 1/25 = 1/9.375 }}}
{{{ .0667 + .04 = .10667 }}}
{{{ .1067 = .10667 }}}
OK