A water tap fills a tub in 'p' hours and a sink at the bottom empties it in 'q' hours. If p < q and both tap and sink are opened the tank is filled in 'r' hours, then the relation between p, q, r :
A. $$\frac{1}{r} = \frac{1}{p} + \frac{1}{q}$$
B. $$\frac{1}{r} = \frac{1}{p} - \frac{1}{q}$$
C. $$r{\text{ = }}p{\text{ }} + {\text{ }}q$$
D. $${\text{ }}r{\text{ }} = {\text{ }}p{\text{ }} - {\text{ }}q$$
Answer: Option B
Solution(By Examveda Team)
Net efficiency = q - p (∵ q > p)
Time required
$$\eqalign{ & {\text{r}} = \frac{{pq}}{{q - p}} \cr & or\,\frac{1}{r} = \frac{1}{p} - \frac{1}{q} \cr} $$
Related Questions on Pipes and Cistern
A. $$\frac{5}{{11}}$$
B. $$\frac{6}{{11}}$$
C. $$\frac{7}{{11}}$$
D. $$\frac{8}{{11}}$$
A. $$1\frac{{13}}{{17}}$$ hours
B. $$2\frac{8}{{11}}$$ hours
C. $$3\frac{9}{{17}}$$ hours
D. $$4\frac{1}{2}$$ hours
A. $$4\frac{1}{3}$$ hours
B. 7 hours
C. 8 hours
D. 14 hours
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