Question 632751
Add the rates of filling
Let one pipe's rate = ( 1 pool filled ) / ( x hours )
The other pipe's rate = ( 1 pool filled ) / ( 8 hours )
Both pipes together = ( 1 pool filled ) / ( 4 and 48/60 hrs )
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{{{ 1/8 + 1/x = 1/(24/5) }}}
{{{ 1/8 + 1/x = 5/24 }}}
Multiply both sides by {{{ 24x }}}
{{{ 3x + 24 = 5x }}}
{{{ 2x = 24 }}}
{{{ x = 12 }}}
The other pipe takes 12 hrs to fill the pool
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check:
{{{ 1/8 + 1/12 = 5/24 }}}
{{{ 3/24 + 2/24 = 5/24 }}}
{{{ 5/24 = 5/24 }}}
OK