Question 547846
Add their rates of filling
1st pipe's rate = ( 1 tank ) / ( 12 hrs )
2nd pipe's rate = ( 1tank ) / ( 8 hrs )
Let {{{t}}} = hrs to fill tank using both pipes
{{{ 1/12 + 1/8 = 1/t }}}
Multiply both sides by {{{ 24t }}}
{{{ 2t + 3t = 24 }}}
{{{ 5t = 24 }}}
{{{ t = 4.8 }}}
{{{ .8*60 = 48 }}}
It will take 4 hrs and 48 min with both pipes