# Math Help - PROBABILITY problems help please

1. ## PROBABILITY problems help please

1) A five-digit number is created using the digits 1-5 each once. What is the probability that the number is odd? Express your answer as a common fraction.

2) The sum of the digits of a number is 9. What is the
probability that the number is prime?

2. #1:

$\frac{5^{4}\cdot 3}{5^{5}}=\frac{3}{5}$

As Plato pointed out, I made a mistake and overlooked your problem said, 'each digit appears once'. Instead of deleting it, let's just say this is the case where the digits repeat.

3. Originally Posted by sri340
1) A five-digit number is created using the digits 1-5 each once. What is the probability that the number is odd? Express your answer as a common fraction.

2) The sum of the digits of a number is 9. What is the
probability that the number is prime?
Originally Posted by galactus
#1:
$\frac{5^{4}\cdot 3}{5^{5}}=\frac{3}{5}$
That answer is for numbers with repeated digits.
The problem says "each once".
Try $\frac{4!\cdot 3}{5!}$

#2 hint If the sum of the digits is multiple of three the the number is divisiable by three.

4. Oh, I overlooked that.

Thanks.