Question 809360
Let {{{ t }}} = time in hrs for the other pipe to 
fill the pool by itself
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Add their rates of filling to get the rate filling together
( 1 pool filled ) / ( 3 hrs ) + ( 1 pool filled ) / ( t hrs ) = ( 1 pool filled ) / ( 1.5 hrs )
{{{ 1/3 + 1/t =  1/1.5 }}}
Multiply both sides by {{{ 3t }}}
{{{ t + 3 = 2t }}}
{{{ t = 3 }}}
The other pipe can fill the pool by itself in 3 hrs also
check:
{{{ 1/3 + 1/3 = 1/1.5 }}}
{{{ 2/3 = 1/1.5 }}}
Multiply both sides by {{{ 3 }}}
{{{ 2 = 2 }}}
OK