Question 824909
Here is the correction of the first tutor's method, using draining rate
instead of filling rate:
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The rate of DRAINING the tank is when all pipes are open,
{{{-1/18-1/27+1/6=1/(2*3*3)-1/(3*3*3)+1/(2*3)=-3/(54)-2/54+9/54=highlight(2/27)}}}, tanks per minute.


The tank at 2/3 full and having all three pipes open would be drained
when m minutes pass:  {{{(2/27)*m=2/3}}}
{{{m=(2/3)(27/2)}}}
{{{m=9}}} minutes
<pre>
Edwin</pre>