Question 505955
Add the rate of filling
( 1 tank / 20 min ) + ( 1 tank / 30 min ) + ( 1 tank / 60 min ) = ( 1 tank / x min )
{{{ 1/20 + 1/30 + 1/60 = 1/x }}}
Multiply both sides by {{{ 60x }}}
{{{ 3x + 2x + x = 60 }}}
{{{ 6x = 60 }}}
{{{ x = 10 }}}
It will take 10 min to fill tank with all 3 pipes