Question 916641
Add their rates of working to get
their rate working together
John Jr's rate: ( 180 boxes ) / ( 1 hr )
John Sr's rate: ( 20 boxes ) / ( 1 hr )
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Let {{{ t }}} = time in hrs for them to
construct {{{ 600 }}} boxes working
together
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{{{ 180/1 + 20/1 = 600 / t }}}
Multiply both sides by {{{ t }}}
{{{ 180t + 20t = 600 }}}
{{{ 200t = 600 }}}
{{{ t = 3 }}}
{{{ 3*60 = 180 }}}
It will take them 180 min working together
check:
{{{ 180/1 + 20/1 = 600 / 3 }}}
{{{ 200 = 600/3 }}}
{{{ 200 = 200 }}}
OK