Question 615267
You must add their rates of working to get
their rate working together
Brian's rate: ( 1 driveway ) / ( 30 min )
Brian's rate + Alan's rate: ( 1 driveway ) / ( 20 min )
Let Alan's rate working alone = ( 1 driveway / x min )
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{{{ 1/30 + 1/x = 1/20 }}}
Multiply both sides by {{{ 60x }}}
{{{ 2x + 60 = 3x }}}
{{{ x = 60 }}}
Alan can do the job alone in 1 hour