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Question
For a loaded die, the probabilities of outcomes are given as under:
P(1) = P(2) = 0.2, P(3) = P(5) = P(6) = 0.1 and P(4) = 0.3. The die is thrown two times. Let A and B be the events, ‘same number each time’, and ‘a total score is 10 or more’, respectively. Determine whether or not A and B are independent.
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Solution
A loaded die is thrown such that P(1) = P(2) = 0.2, P(3) = P(5) = P(6) = 0.1 and P(4) = 0.3 and die is thrown two times.
Also given that: A = Same number each time and
B = Total score is 10 or more.
So, P(A) = [P(1, 1) + P(2, 2) + P(3, 3) + P(4, 4) + P(5, 5) + P(6, 6)]
= P(1).P(1) + P(2).P(2) + P(3).P(3) + P(4).P(4) + P(5).P(5) + P(6).P(6)
0.2 × 0.2 + 0.2 × 0.2 + 0.1 × 0.1 + 0.3 × 0.3 + 0.1 × 0.1 + 0.1 × 0.1
= 0.04 + 0.04 + 0.01 + 0.09 + 0.01 + 0.01 = 0.20
Now B = [(4, 6), (6, 4), (5, 5), (5, 6), (6, 5), (6, 6)]
P(B) = [P(4).P(6) + P(6).P(4) + P(5).P(5) + P(5).P(6) + P(6).P(5) + P(6).P(6)
= 0.3 × 0.1 + 0.1 × 0.3 + 0.1 × 0.1 + 0.1 × 0.1 + 0.1 × 0.1 + 0.1 × 0.1
= 0.03 + 0.03 + 0.01 + 0.01 + 0.01 + 0.01 = 0.10
A and B both events will be independent if
P(A ∩ B) = P(A).P(B) ......(i)
Here, (A ∩ B) = {(5, 5), (6, 6)}
∴ P(A ∩ B) = P(5, 5) + P(6, 6) = P(5).P(5) + P(6).P(6)
= 0.1 × 0.1 + 0.1 × 0.1
= 0.02
From equation (i) we get
0.02 = 0.20 × 0.10
0.02 = 0.02
Hence, A and B are independent events.
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