Question 1083155
Add their rates of shoveling to get their
rate shoveling together
student's rate:
[ 1 driveway shoveled / 20 min ]
brother's rate:
[ 1 driveway shoveled / 12 min ]
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Let {{{ t }}} = their time to shovel the
driveway working together
{{{ 1/20 + 1/12 = 1/t }}}
Multiply both sides by {{{ 60t }}}
{{{ 3t + 5t  = 60 }}}
{{{ 8t = 60 }}}
{{{ t = 7.5 }}}
They can shovel the driveway in 7.5 min, which
is less than 10 min needed