1.

Two fair dice are thrown. State the sample space and write the favourable outcomes for the following events. (a) A : Sum of numbers on two dice is divisible by 3 or 4. (b) B : The sum of numbers on two dice is 7. (c) C : Odd number on the first die. (d) D : Even number on the first die. (e) Check whether events A and B are mutually exclusive and exhaustive. (f) Check whether events C and D are mutually exclusive and exhaustive.

Answer»

When two dice are thrown, the sample space is 

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

(a) A: Sum of the numbers on two dice is divisible by 3 or 4. 

∴ A = {(1, 2), (1, 3), (1, 5), (2, 1), (2, 2), (2, 4), (2, 6), (3, 1), (3, 3), (3, 5), (3, 6), (4, 2), (4, 4), (4, 5), (5, 1), (5, 3), (5, 4), (6, 2), (6, 3), (6, 6)} 

(b) B: Sum of the numbers on two dice is 7. 

∴ B = {(1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1)} 

(c) C: Odd number on the first die. 

∴ C = {(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6), (3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6), (5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6)} 

(d) D: Even number on the first die. 

∴ D = {(2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6), (4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6), (6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)} 

(e) A and B are mutually exclusive events as A ∩ B = Φ. 

A ∪ B = {(1, 2), (1, 3), (1, 5), (1, 6), (2, 1), (2, 2), (2, 4), (2, 5), (2, 6), (3, 1), (3, 3), (3, 4), (3, 5), (3, 6), (4, 2), (4, 3), (4, 4), (4, 5), (5, 1), (5, 2), (5, 3), (5, 4), (6, 1), (6, 2), (6, 3), (6, 6)} ≠ S 

∴ A and B are not exhaustive events as A ∪ B ≠ S. 

(f) C and D are mutually exclusive events as C ∩ D = Φ. 

C ∪ D = {(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)} = S 

∴ C and D are exhaustive events.



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