Question

Primes are numbers divisible only by 1 and themselves; There are infinitely many prime numbers and the first ones are 2, 3, 5, 7, 11, 13, 17, 19, 23, .... Consider a 12-sided die, with the faces numbered from 1 to 12. Out of 4 rolls, the probability that only the first three numbers are primes is:

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Eliseo

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56 Answers

From 1 to 12, the number of prime number is 5 (2,3,5,7,11) and the number of not a prime number is 7 (1,4,6,8,9,10,12)
1st roll is prime = 5/12
2nd roll is prime = 5/12
3rd roll is prime = 5/12
4th roll is not prime = 7/12
So the probability is \frac{5}{12}\frac{.5}{12}\frac{.5}{12}\frac{.7}{12}=\frac{875}{20736}=0.0422
That's the answer.

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