Question 667143
If the 1st group can do 1 job in 8 days,
they do 1/8 of the job in 1 day
So, in 3 days they do 3/8 of the job
That means 5/8 of the job is left to be done
------------------
Let {{{ d }}} = the number of days the 2nd
group takes to do the job alone.
Add their rates of working to get the rate
at which they can do the 5/8 of a job working together
{{{ 1/8 + 1/d = (5/8)/3 }}}
{{{ 1/8 + 1/d = 5/24 }}}
Multiply both sides by {{{ 24d }}}
{{{ 3d + 24 = 5d }}}
{{{ 2d = 24 }}}
{{{ d = 12 }}}
The 2nd group could have done the job alone in 12 days