A fair die is rolled three times. The probability that you get a larger number each time is , where and are coprime positive integers. What is a+b?
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When a die is rolled 3 times, there are 6 · 6 · 6 = 216 possible outcomes. If a 1 is rolled first, then there are 10 possible outcomes for the next two digits such that the third digit is greater than the second, which is greater than the first. If a 2 is rolled first, then there are 6 possible outcomes for the next two digits where the digits increase. If a 3 is rolled first , there are 3 ways for the digits to increase, and if a 4 is rolled first, there is 1 way for digits to increase. So there are a total of 10 + 6 + 3 + 1 = 20 total outcomes. Thus the probability is 2 1 6 2 0 = 5 4 5 .
5 + 5 4 = 5 9 .