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counting and probability intermediate
Problem
A fair -sided die is repeatedly rolled until an odd number appears. What is the probability that every even number appears at least once before the first occurrence of an odd number?
(A)
(B)
(C)
(D)
Solution
Since 3 out of 6 of the numbers are even, there is a chance that the first number we choose is even. Since the number rolled first is irrelevant, we don't have to consider it. Therefore there are 2 even numbers out of the 5 choices left. There is a chance that the next number that is distinct from the first is even. There is a chance that the next number distinct from the first two is even. (There is only one even integer left. ) With all the even integers taken, the next integer rolled must be odd. , so the answer is
Final answer
C