Beautiful question on probability try to solve it


There are four machines and it is known that exactly 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 required is

a) (1/2)
b) (1/3)
c) (1/4)
d) (1/6)


The answer is D since the two events are independent events. So you can say (2/4) * (1/3). Am I correct