The gambler de Mere asked Pascal whether it is more likely to get at least one six in 4

Chapter 4, Problem 76

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The gambler de Mere asked Pascal whether it is more likely to get at least one six in 4 rolls of a die, or to get at least one double-six in 24 rolls of a pair of dice. Continuing this pattern, suppose that a group of n fair dice is rolled 4 6n1 times. (a) Find the expected number of times that all sixes is achieved (i.e., how often among the 4 6n1 rolls it happens that all n dice land 6 simultaneously). (b) Give a simple but accurate approximation of the probability of having at least one occurrence of all sixes, for n large (in terms of e but not n). (c) de Mere finds it tedious to re-roll so many dice. So after one normal roll of the n dice, in going from one roll to the next, with probability 6/7 he leaves the dice in the same configuration and with probability 1/7 he re-rolls. For example, if n = 3 and the 7th roll is (3, 1, 4), then 6/7 of the time the 8th roll remains (3, 1, 4) and 1/7 of the time the 8th roll is a new random outcome. Does the expected number of times that all sixes is achieved stay the same, increase, or decrease (compared with (a))? Give a short but clear explanation.