Question 1026600
Find out how long it will take them both
to was 1 car. It will take 20 times longer
to wash 20 cars
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Joe's rate of working:
[  1 car washed ] / [ 4 hrs ]
Sam's rate of working:
[ 1 car washed ] / [ 6 hrs ]
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Let {{{ t }}} = time in hrs for them to
wash 1 car working together
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Add their rates of working to get their rate working together
{{{ 1/4 + 1/6 = 1/t }}}
Multiply both sides by {{{ 12t }}}
{{{ 3t + 2t = 12 }}}
{{{ 5t = 12 }}}
{{{ t = 12/5 }}} hrs to wash 1 car working together
Now multiply by {{{ 20 }}} for 20 cars
{{{ 20*( 12/5 ) = 48 }}}
Working together, it will take them 48 hrs
to wash 20 cars
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A good rule to remember is that, working together, it
always takes less time than the fastest of the
2 workers