Question 746589
Add their rates of working to get their
rate working together
1st man's rate: ( 1 job ) / ( 10 hrs )
Both men working together: ( 1 job ) / ( 4 hrs )
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Let {{{ t }}} = the time in hours for the 2nd
man to do the job alone
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{{{ 1/10 + 1/t = 1/4 }}}
Multiply both sides by {{{ 20t }}}
{{{ 2t + 20 = 5t }}}
{{{ 3t = 20 }}}
{{{ t = 6.667 }}} hrs
{{{ .667*60 = 40 }}} min
It takes the 2nd man 6 hrs and 40 min to do the job alone