Question 1083622
All 3 work at the same rate:
In words, the rate is:
[ job done, or fraction of the job done  ] / [ the time to do it ]
---------------------------------------
Let {{{ t }}} = time for either Greg or Joan to do 1 job
I can add their rates of working to get their rate
working together
-----------------------------
{{{ 1/t + 1/t = 1/8 }}}
{{{ 2*( 1/t ) = 1/8 }}}
{{{ 1/t = 1/16 }}}
{{{ t = 16 }}}
--------------------------
For all 3 friends:
Let {{{ T }}} = time to finish the job if
all 3 work on it
{{{ 1/t + 1/t + 1/t = 1/T }}}
{{{ 3*( 1/16 ) = 1/T }}}
Multiply both sides by {{{ 16T }}}
{{{ 3T = 16 }}}
{{{ T = 16/3 }}}
It will takes them 3 and 1/3 days working together
---------------------------
Get another opinion on this if needed