GATE | GATE CS Mock 2018 | Set 2 | Question 51

In a bunch of 13 T-shirts only one is of Medium size, which is correct fit for the searching person. Each time wrong size is picked, the person throws it away and pick the next T-shirt. What is the probability that the correct size T-shirt can be searched in 8th attempt ?

(A) 1/1287
(B) 1/330
(C) 5/13
(D) 1/13


Answer: (D)

Explanation: Let Li be the event of searching medium sized T-shirt in ith attempt.

P(L'1 ∩ L'2 ∩ L'3 ∩ L'4 ∩ L'5 ∩ L'6 ∩ L'7 ∩ L8 ) 
= 12/13 . 11/12. 10/11. 9/10. 8/9. 7/8. 6/7. 1/6
= 1/13 

So, option (D) is correct.

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