Here we have selected positive numbers from 2 to 18 so there are total 17 numbers with us.
Now the prime numbers between 2 and 17 are
2, 3, 5, 7, 11, 13, 17
So there are 7 prime numbers between 2 to 18
We have to find the probability of selecting prime numbers between 2 to 18
Probability = Outcomes of interest / All possible outcomes
Probability prime = 7/17
Probability prime = 0.4117
So probability of getting prime number is 0.4117