Question 808858
Add their rates of working to get their
rate working together
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Susan's rate:
( 1 garden planted ) / ( 5 hrs )
Friend's rate:
( 1 garden planted ) / ( 8 hrs )
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Let {{{ t }}} = the time in hours to 
plant a garden working together
{{{ 1/5 + 1/8 = 1/t }}}
Multiply both sides by {{{ 40t }}}
{{{ 8t + 5t = 40 }}}
{{{ 13t = 40 }}}
{{{ t = 3.077 }}}
{{{ .077*60 = 4.62 }}}
It will take them about 3 hrs 4.6 min