Question 1080749
Tina's rate of working:
[ 1 garden weeded ] / [ 20 min ]
Marisa's rate of working:
[ 1 garden weeded ] / [ 50 min ]
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Add their rates of working to get their rate
working together, which is:
[ 1 garden weeded ] / [ t min ]
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{{{ 1/20 + 1/50 = 1/t }}}
Multiply both sides by {{{ 100t }}}
{{{ 5t + 2t = 100 }}}
{{{ 7t = 100 }}}
{{{ t = 14 + 2/7 }}}
{{{ (2/7)*60 = 17.14 }}}
Working together, it will take them
14 min 17 sec
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check:
{{{ 1/20 + 1/50 = 1/(100/7) }}} 
{{{ .05 + .02 = .07 }}}
OK