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One ticket is drawn from a purse containing four tickets with numbers 223, 133, 212, 322. Let AiA_i be the event that ith^{th} digit of the number on drawn ticket is 2. Then which of the following events are independent ?

A. A1A_1 and A2A_2

B. A2A_2 and A3A_3

C. A1A_1 and A3A_3

D. A1A_1, A2A_2 and A3A_3

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

Each of A1A_1, A2A_2, A3A_3 occurs on exactly two tickets, so each has probability 12\dfrac{1}{2}.

Each pair occurs on exactly one ticket: A1∩A2={223}A_1\cap A_2 = \{223\}, A2∩A3={322}A_2\cap A_3=\{322\}, A1∩A3={212}A_1\cap A_3=\{212\}, each with probability 14=12⋅12\dfrac{1}{4} = \dfrac{1}{2}\cdot\dfrac{1}{2}, so all pairs are independent.

No ticket is 222, so P(A1∩A2∩A3)=0≠18P(A_1\cap A_2\cap A_3)=0 \ne \dfrac{1}{8}; mutual independence fails.

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