Question 973876
Add their rates of washing to get
their rate washing together
George's rate:
[ 1 car ] / [ 20 min ]
Sally's rate:
[ 1 car ] / [ 15 min ]
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Let {{{ t }}} = time in minutes working together
{{{ 1/20 + 1/30 = 1/t }}}
Multiply both sides by {{{ 60t }}}
{{{ 3t + 2t = 60 }}}
{{{ 5t = 60 }}}
{{{ t = 12 }}} min
It takes them 12 min working together