Question 1067097
Add their rates of painting to get their
rate painting together
Call the room to be painted [ 1 job ]
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Neil's rate:
[ 1 job ] / [ 6.75 hrs ]
Den's rate:
[ 1 job ] / [ 4.5 hrs ]
Let their rate painting together = 
[ 1 job ] / [ t hrs ]
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{{{ 1/6.75 + 1/4.5 = 1/t }}}
Multiply both sides by {{{ 6.75*4.5*t }}}
{{{ 4.5t + 6.75t = 6.75*4.5 }}}
{{{ 4.5t + 6.75t = 30.375 }}}
{{{ 11.25t = 30.375 }}}
{{{ t = 2.7 }}}
Painting together, it will take them 2.7 hrs