InterviewSolution
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Two dice are thrown together. What is the probability that sum numbers on the two faces is neither divisible by 3 nor 4? |
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Answer» Let ‘S’ be the sample space. ∴ S = {(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6), (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6), (6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)}. ⇒ n(S) = 36 Let ‘A’ and ‘B’ be the events that the sum of the numbers on the two faces is divisible by 3 and 4 respectively. ∴ A = {(1, 2), (1, 5), (2, 1), (2, 4), (3, 3), (3, 6), (4, 2), (4, 5), (5, 1), (5, 4), (6, 3), (6, 6)} ⇒ n(A) = 12 and, B = {(1, 3), (2, 2), (2, 6), (3, 5), (4, 4), (5, 3), (6, 2), (3, 1), (6, 6)} ⇒ n(B) = 9 ∴ P(A) = \(\frac{n(A)}{n(S)}=\frac{12}{36}\) P(B) = \(\frac{n(A)}{n(S)}=\frac{12}{36}\) P(B) = \(\frac{n(B)}{n(S)}=\frac{9}{36}\) A ∩ B = {(6, 6)} ⇒ n(A ∩ B) = 1 ∴ (A ∩ B) = \(\frac{n(A∩ B)}{n(S)}=\frac{1}{36}\) We know– P(A ∪ B) = P(A) + P(B) – P(A ∩ B) = \(\frac{13}{36}+\frac{9}{36}-\frac{1}{36}=\frac{20}{36}=\frac{5}{9}\) ∴ Probability of getting the sum multiple of 3 or 4 is \(\frac{5}{9}\) ⇒ Probability of getting the sum neither a multiple of 3 nor 4 = P(A ∪ B) = \(p(\overline{A∪B})\) = 1 – P(A ∪ B) \(= 1 - \frac{5}{9}\) = \(\frac{4}{9}\) |
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