Engineering
Mathematics
Addition Theorem on Probability
Basic Definitions Related to Probability
Question

Let two fair six‑faced dice A and B be thrown simultaneously. If E1 is the event that die A shows up four, E2 is the event that die B shows up two and E3 is the event that the sum of numbers on both dice is odd, then which of the following statements is NOT true?

E1 and E2 are independent.

E2 and E3 are independent.

E1, E2 and E3 are independent.

E1 and E3 are independent.

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Solution

E1 : {(4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6)}

E2 : {(1, 2), (2, 2), (3, 2), (4, 2), (5, 2), (6, 2)}

E3 : {(1, 2), (1, 4), (1, 6), (3, 2), (3, 4), (3, 6), (5, 2), (5, 4), (5, 6), (2, 1), (2, 5), (4, 1), (4, 3), (4, 5), (6, 1), (6, 3), (6, 5)}

P(E1)=636=16;  P(E2)=636=16

P(E3)=1836=12

P(E1  E2) = 136 = P(E1) P(E2)

⇒ E1 & E2 are independent

P(E2  E3) = 336=112= P(E1) P(E3)

⇒ E2 & E3 are independent

P(E1  E3) = 336=112= P(E1) P(E3)

⇒ E1 & E3 are independent

P(E1  E2  E3) = 0   P(E1) P(E2) P(E3).

⇒ E1, E2 & E3 are not independent.