Question 921387
Rate of filling:
{{{ 1/15 }}} tanks / min
Rate of draining:
{{{ 1/45 }}} 
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Let {{{ t }}} = time in min to fill tank
{{{ 1/15 - 1/45 = 1/t }}}
Multiply both sides by {{{ 45t }}}
{{{ 3t - t = 45 }}}
{{{ 2t = 45 }}}
{{{ t = 22.5 }}}
It takes 22.5 min to fill tank
and
{{{ .5*60 = 30 }}}
It takes 22 min 30 sec to fill tank