"one fifth of the light switches"..
I agree with everything in the explanation EXCEPT the total number of NON DEFECTIVE light switches which should be 20. Please read the wording in the question very carefully:
1/4 of the non-defective switches are rejected by mistake" There are a total of 80 non defective light switches if you assume a total of 100 light switches total. The answer should be C?

Can you please point me to a place on veritasprep where the errata's are posted for all the blue books?

100 switches

20 defective
16 rejected
4 not rejected


80 non defective
4 rejected
76 not rejected


all the "not rejecteds" 4 + 76 are sold

4/(4 + 76) = 1/20 = 5%

There is a section of True Track for errata

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