Read the two statements and choose the correct option.
I. An inlet fills a tank in $a$ hours and an outlet empties it in $b$ hours, with $b > a$ . With both open, the empty tank fills in $\frac{ab}{b - a}$ hours.
II. If instead $b < a$ , the empty tank still fills in the end, only more slowly.

Only ICorrect answerYour answerOnly IICorrect answerYour answerBoth I and IICorrect answerYour answerNeither I nor IICorrect answerYour answer

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CorrectNot quiteAnswer A

Correct answer: A

I: net rate $\frac{1}{a} - \frac{1}{b} = \frac{b - a}{ab}$ , positive when $b > a$ , so the time is $\frac{ab}{b - a}$ . True.
II: when $b < a$ the outlet drains faster than the inlet fills, so the tank never fills. False.

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