1974 AHSME Problems/Problem 24
Problem
A fair die is rolled six times. The probability of rolling at least a five at least five times is
Solution
The probability of rolling at least a five on any one roll is . If there are exactly fives or sixes rolled, there are ways to pick which of the rolls are the fives and sixes, and so the probability in this case is . If there are exactly fives or sixes rolled, then there is only one way to pick which of the rolls are fives and sixes, so the probability in this case is .
Therefore, the total probability is .
See Also
1974 AHSME (Problems • Answer Key • Resources) | ||
Preceded by Problem 23 |
Followed by Problem 25 | |
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