Question : A water tap fills a tub in '$p$' hours and a sink at the bottom empties it in '$q$' hours. If $p < q$, both tap and sink are open, and the tank is filled in '$r$' hours, then:
Option 1: $\frac{1}{r}$ = $\frac{1}{p}+\frac{1}{q}$
Option 2: $\frac{1}{r}$ = $\frac{1}{p}-\frac{1}{q}$
Option 3: $r = p + q$
Option 4: $r = p - q$
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Correct Answer: $\frac{1}{r}$ = $\frac{1}{p}-\frac{1}{q}$
Solution : Given: A water tap fills a tub in '$p$' hours and a sink at the bottom empties it in '$q$' hours where $p < q$. So, in 1 hour the tap will fill $\frac{1}{p}$ part of the tub. Also, in 1 hour the sink will empty $\frac{1}{q}$ part of the tub. Now, part of the tub that will fill in 1 hour with both of them opened = ($\frac{1}{p}-\frac{1}{q}$) Time taken to fill the whole tub = $\frac{1}{(\frac{1}{p}–\frac{1}{q})}$ hours, which is equal to $r$. Therefore, $\frac{1}{(\frac{1}{p}–\frac{1}{q})}$ = $r$ ⇒ $\frac{1}{r}$ = $\frac{1}{p}-\frac{1}{q}$ Hence, the correct answer is $\frac{1}{r}$ = $\frac{1}{p}-\frac{1}{q}$.
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Question : If $P =\frac{96}{95\times97}, Q = \frac{97}{96\times98}$ and $R = \frac{1}{97}$, then which of the following is true?
Option 1: $P < Q < R $
Option 2: $R < Q < P $
Option 3: $Q < P < R $
Option 4: $R < P < Q $
Question : An inlet pipe can fill an empty tank in $4 \frac{1}{2}$ hours, while an outlet pipe drains a filled tank in $7 \frac{1}{5}$ hours. The tank is initially empty, and the two pipes are alternately opened for an hour each, till the tank is filled, starting with the inlet pipe. In how many hours will the tank be filled?
Option 1: 24 hours
Option 2: $20 \frac{1}{4}$ hours
Option 3: $20 \frac{3}{4}$ hours
Option 4: $22 \frac{3}{8}$ hours
Question : A tap can fill a tank in $5 \frac{1}{2}$ hours. Because of a leak, it took $8 \frac{1}{4}$ hours to fill the tank. In how much time (in hours) will the leak alone empty 30% of the tank?
Option 1: $\frac{99}{20}$
Option 2: $\frac{5}{2}$
Option 3: $\frac{9}{2}$
Option 4: $\frac{17}{2}$
Question : The value of $ \frac{(p-q)^3+(q-r)^3+(r-p)^3}{12(p-q)(q-r)(r-p)}$, where $p \neq q \neq r$, is equal to:
Option 1: $\frac{1}{9}$
Option 2: $\frac{1}{3}$
Option 3: $\frac{1}{4}$
Option 4: $\frac{1}{2}$
Question : Two pipes, S1 and S2, can alone fill an empty tank in 15 hours and 20 hours, respectively. Pipe S3 alone can empty that filled tank in 40 hours. Firstly, both pipes, S1 and S2, are opened and after 2 hours, pipe S3 is also opened. In how much time will the tank be filled after S3 is opened?
Option 1: $\frac{90}{17}\ \text{hours}$
Option 2: $\frac{89}{12}\ \text{hours}$
Option 3: $\frac{90}{13}\ \text{hours}$
Option 4: $\frac{92}{11}\ \text{hours}$
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