probability problem

Question

an urn contains tags with numbers 1 to 25. one tag is picked t random. find the probabilities of the occurrence of the following events:

1. odd number
2. number 18
3. number divisible by 3 
4. a prime number (a number, >1, divisible only by itself and 1)
5. a number divisible by 2 or 3 (or both).

Answer 1

in the set 1 ... 25 there are 13 odd numbers and 12 evens.

1) P(odd) = 13/25

2) P("18") = 1/25

3) there are 8 numbers divisible by 3 and ≤25 so P(divisible by 3) = 8/25

4) count how many primes are  ≤25, remembering that 2 is the lowest prime...then YOU figure this probability.

5) count how many primes are ≤25 AND are divisible by 2 or 3 or both...S T E A D Y!!...then YOU figure this probability.