p = 1/6

you roll a die and wait for the number 5 on the die.

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- May 21st 2007, 09:07 AMshirelprobability: rolling a die
p = 1/6

you roll a die and wait for the number 5 on the die. - May 21st 2007, 11:02 AMThePerfectHacker
Instead consider what is the probability of NOT getting a 5. It is 5/6 if you do that n times you have (5/6)^n.

Hence, the probability of getting at least one 5 is 1-(5/6)^n

We want this to be expected, i.e,

1-(5/6)^n >= 1/2

Thus,

(5/6)^n <= 1/2

Find the first value of n which makes this true.