Question 889347
Add their rates of printing
Jim's:
( 1 job ) / ( 7 hrs )
Janet's:
( 1 job ) / ( 12 hrs )
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Let {{{ t }}} = time in hours for
both printers to do the job
{{{ 1/7 + 1/12 = 1/t }}}
Multiply both sides by {{{ 7*12*t }}}
{{{ 12t + 7t = 7*12 }}}
{{{ 19t = 84 }}}
{{{ t = 84/19 }}}
{{{ t = 4 + 8/19 }}}
{{{ ( 8/19 )*60 = 25.26 }}}
{{{ .26*60 = 16 }}}
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It will take both copiers 4 hrs 25 min 16 sec
check answer:
{{{ 1/7 + 1/12 = 1/t }}}
{{{ 1/7 + 1/12 = 1/(84/19) }}} 
{{{ 1/7 + 1/12 = 19/84 }}}
{{{ 12/84 + 7/84 = 19/84 }}}
{{{ 19/84 = 19/84 }}}