Question 988327
Add their rates of cleaning to get rate working together
Benny's rate:
[ 1 attic cleaned ] / [ 8 hrs ]
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Donna's rate:
[ 1 attic cleaned ] / [ t hrs ]
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Rate working together:
{{{ 1/8 + 1/t = 1/5 }}}
Multiply both sides by {{{ 40t }}}
{{{ 5t + 40 = 8t }}}
{{{ 3t = 40 }}}
{{{ t = 13.333 }}} hrs
Note that {{{ (1/3)*60 = 20 }}} min
Working alone, Donna would take
13 hrs and 20 min to clean the attic
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check answer:
{{{ 1/8 + 1/t = 1/5 }}}
{{{ 1/8 + 1/13.333 = 1/5 }}}
{{{ .125 + .075 = .2 }}}
{{{ .2 = .2 }}}
OK