Question 560352
just use the same ratio
{{{ (5/8) / 3 }}} job/days
Multiply top and bottom by {{{ 8/5 }}}
{{{ 1 / ((8/5)*3) }}}
{{{ 1 / (24/5) }}}
This is 1 job completed in 4 and 4/5 days
This makes sense, because it will take a little longer 
than 3 days if 5/8 of the job is done in 3 days
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How much of the job can B get done in 3 days?
B's rate = {{{ 1/12 }}} job/days. This is the same as
{{{ (1/12) / 1 }}} job/days
In 3 days B will get 3 times as much done, or
{{{ 3/12 = 1/4 }}} job
Now A has to do {{{ 3/4 }}} of the job to finish it
A's rate = {{{ 1/8 }}}  job/days
Note that ( days ) = ( job ) / ( job/days ) )
{{{ ( 3/4) / ( 1/8 ) = 24/4 }}}
{{{ 24/4 = 6 }}}
It will take A 6 days to finish the job alone