i'm horrible in mathemantics...can some help with this question. find the probability that in FOUR tosses of a fair die a 3 appears

a)exactly no (zero)time

b)exactly three times

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- June 28th 2008, 03:48 PMbklyngrkbellaprobability
i'm horrible in mathemantics...can some help with this question. find the probability that in FOUR tosses of a fair die a 3 appears

a)exactly no (zero)time

b)exactly three times - June 28th 2008, 06:47 PMmr fantastic
The probability of getting a 3 in a single roll is 1/6. The probabilty of not getting a 3 in a single roll is 5/6.

a) The probability of 'no 3' is (5/6)^4. You can get 'no 3' in only 1 way. So the probabilty is (1) (5/6)^4 = ......

b) The probability of 'exactly three 3's' is (1/6)^3 (5/6). You can get 'three 3's' in four different ways:

3, 3, 3, x

3, 3, x, 3

3, x, 3, 3

x, 3, 3, 3.

So the probability is (4) (1/6)^3 (5/6) = ......