Question 785797
Add their rates of painting to get the
rate of all 3painting together
( 1 room )/( 3 hrs ) + ( 1 room )/( 4 hrs ) + ( 1 room )/( 6 hrs )
= ( 1 room )/( t hrs )
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{{{ 1/3 + 1/4 + 1/6 = 1/t }}}
Multiply both sides by {{{ 12t }}}
{{{ 4t + 3t + 2t = 12 }}}
{{{ 9t = 12 }}}
{{{ t = 4/3 }}}
{{{ 4/3 = 1 + 1/3 }}}
{{{ (1/3)*60 = 20 }}}
It takes them 1 hr and 20 min to paint
the room together