Question 888491
Let {{{ t }}} = the time in hours for Mary to finish a project
So, Mary's rate of working is ( 1 project / t hrs )
Carol's rate of working is ( 1 project / t/2 hrs )
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Working together, their rate is ( 1 project / 4 hrs )
Add their individual rates of working to get rate working together
{{{ 1/t + 1/(t/2) = 1/4 }}}
{{{ 1/t + 2/t = 1/4 }}}
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As for the amount of work they can finish in {{{ 1 }}} hr,
{{{ 1/t + 2/t = (( 1/4 )) / 1 }}}