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NCERT Class XI Mathematics - Probability - Solutions
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Question : 23 of 54
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Refer to question 6 above, state true or false : (give reason for your answer). (i) A and B are mutually exclusive (ii) A and B are mutually exclusive and exhaustive (iii) A = B′ (iv) A and C are mutually exclusive (v) A and B′ are mutually exclusive. (vi) A′, B′, C are mutually exclusive and exhaustive.
Solution:
(i) True. A = getting an even number on the first die. B = getting an odd number on the first die. There is no common elements in A and B. ⇒ A ∩ B = ϕ ∴ A and B are mutually exclusive. (ii) True. From (i), A and B are mutually exclusive. A ∪ B = {(1, 1), (1, 2), ...., (1, 6), (2, 1), (2, 2), ..., (2, 6), ..., (6, 1), (6, 2), ..., (6, 6) = S ∴ A ∪ B is mutually exhaustive. (iii) True. B = getting an odd number on the first die. B′ = getting an even number on first die = A. ∴ A = B′ (iv) False. Since A ∩ C = {(2, 1), (2, 2), (2, 3), (4, 1)} ≠ϕ (v) False. Since B′ = A [from (iii)] ∴ A ∩ B′ = A ∩ A = A ≠ϕ (vi) False. Since A′ = B and B′ = A, A′ ∩ B′ = ϕ B ∩ C = {(1, 1), (1, 2), (1, 3), (1, 4), (3, 1), (3, 2)} ≠ϕ A ∩ C = {(2, 1), (2, 2), (2, 3), (4, 1)} ≠ϕ Thus A′, B′ and C are not mutually exclusive.
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