Question 1088529
The man's rate of working is
[ 1 room painted ] / [ 8 hrs ] = {{{ 1/8 }}}
-------------------------------------
[ rate ] x [ time in hrs ] = [ fraction of the job completed ]
{{{ (1/8)*2 = 1/4 }}}
That means there is {{{ 3/4 }}} of the job left to do
----------------------------------------------------
Add their rates of working to get the rate at which
they will finish 3/4 of the job in {{{ t }}} hrs
{{{ 1/8 + 1/12 = ((3/4)) / t }}}
Multiply both sides by {{{ 24t }}}
{{{ 3t + 2t = 18 }}}
{{{ 5t = 18 }}}
{{{ t = 3.6 }}}
{{{ .6*60 = 36 }}}
The son worked for 3 hrs and 36 min
------------------------------------
Get a 2nd opinion if needed