Question 1042396
Let {{{ t }}} = the time in minutes to
fill the tank with both pipes open
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Add the rate of filling of the filling pipe
and subtract the rate of emptying of
the other pipe
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{{{ 1/15 - 1/40 = 1/t }}}
Multiply both sides by {{{ 120t }}}
{{{ 8t - 3t = 120 }}}
{{{ 5t = 120 }}}
{{{ t = 24 }}}
If both pipes are open, the tank fills in 24 min
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check:
{{{ 1/15 - 1/40 = 1/24 }}}
{{{ .06667 - .025 = .041667 }}}
{{{ .04167 = .041667 }}}
error due to rounding off