There are four machines and it is known that eactly two of them are faulty. They are tested, one by one, in a random order till both the faulty machines are identified. The probability that only two tests are needed is (A) `1/6` (B) `1/3` (C) `1/2` (D) `1/4`A. `(1)/(3)`B. `(1)/(6)`C. `(1)/(2)`D. `(1)/(4)`

There are four machines and it is known that eactly two of them are fa

1.	There are four machines and it is known that eactly two of them are faulty. They are tested, one by one, in a random order till both the faulty machines are identified. The probability that only two tests are needed is (A) `1/6` (B) `1/3` (C) `1/2` (D) `1/4`A. `(1)/(3)`B. `(1)/(6)`C. `(1)/(2)`D. `(1)/(4)`
Answer» Correct Answer - B Probability that only two tests are needed =Probability that the first machine tested is faulty `xx` Probability that the second machine tested is faulty `=(2)/(4)xx(1)/(3)=(1)/(6)`

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