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UPSC Civil Service Exam Questions - Engineering

Q1:

If the efficiencies of BOD removal of first-stage and second-stage trickling filters are each 65.0%, then what is the overall BOD removal efficiency of these filters ?

A 65%

B 77.25%

C 87.75%

D 92.6%

ANS:C - 87.75%

Efficienct = 1 - (1 - n1)(1 - n2) = 1 - (1 - 0.65)(1 - 0.65) = 0.8775 i.e 87.75%.