A) Q alone is open.
B) P and S are open.
C) P, R and S are open.
D) P, Q and S are open.
Correct Answer: D
Solution :
Part of the cistern filled in 1 hour when pipes P and S are open \[=\frac{1}{4}-\frac{1}{10}=\frac{5-2}{20}=\frac{3}{20}\] Hence, the cistern will be filled in \[\frac{20}{3}\] hours. Part of the cistern filled in 1 hour when pipes P, R and S are open \[=\frac{1}{4}+\frac{1}{12}-\frac{1}{10}\] \[=\frac{15+5-6}{60}=\frac{14}{60}=\frac{7}{30}\] Hence, the cistern will be filled in \[\frac{7}{30}\] hours. Part of the cistern filled in I hour when pipes P, Q and S are open \[=\frac{1}{4}+\frac{1}{8}-\frac{1}{10}\] \[=\frac{10+5-4}{40}=\frac{11}{40}\] Hence the cistern will be filled in\[\frac{40}{11}\]Hours. Hence, option [d] is correct.You need to login to perform this action.
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