7. There are four machines and it is known thatexactly two of them are

1.	7. There are four machines and it is known thatexactly two of them are faulity. They are tested,one by one, in a random order till both the faultymachines are identified. Then the probadility thatonely two tests are needed is:
Answer» Solution:(b) 1/6 Explanation:Only 2 testswill be needed to find the faulty machines ifwe can find one faulty machine in eachtest The probability thatwewilltest a faulty machine in the first test is 2/4=1/2 (there are 4 machines and 2 of them faulty) Now that one faulty machine has been identifiedwe are leftwith 3 machineswith one of them being faulty. The probability thatwe will test the other faulty machine in the second test is 1/3. So the probabilitythatwewill require 2 tests to find the faulty machines is 1/2*1/3=1/6

7. There are four machines and it is known thatexactly two of them are faulity. They are tested,one by one, in a random order till both the faultymachines are identified. Then the probadility thatonely two tests are needed is:

Answer»

Solution:(b) 1/6

Explanation:Only 2 testswill be needed to find the faulty machines ifwe can find one faulty machine in eachtest

The probability thatwewilltest a faulty machine in the first test is 2/4=1/2 (there are 4 machines and 2 of them faulty)

Now that one faulty machine has been identifiedwe are leftwith 3 machineswith one of them being faulty. The probability thatwe will test the other faulty machine in the second test is 1/3. So the probabilitythatwewill require 2 tests to find the faulty machines is 1/2*1/3=1/6

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