Volume of water in the tank:

Differentiate both sides with respect to time <em>t</em> :

<em>V</em> changes at a rate of 2000 cc/min (cubic cm per minute); use this to solve for d<em>h</em>/d<em>t</em> :


(The question asks how the height changes at the exact moment the height is 50 cm, but this info is a red herring because the rate of change is constant.)
<span>Divide by 3 get a remainder of 2
5, 8, 11, 14, 17, 20, ...
Divide by 5 get a remainder of 2
7 , 12, 17, 23, ...
Divide by 7 get a reminder of 5
12, 19, 26, 33, ...
And find a number in all three lists
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<span>Not the most convenient way for sure, but since 47 works it will not take too long</span><span>
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4.3125 is the answer to that equation