Question

What is the probability of randomly selecting a prime number from the numbers 1-15?

Answer 1

Sample Space = Set of all possible outcomes
Event Space = Set of outcomes we want to happen (selecting a prime number)

Let,
S = sample space
E = event space

So,
S = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}
E = {2,3,5,7,11,13}
note: 1 is not prime

Furthermore,
n(S) = number of items in set S
n(S) = 15
n(E) = number of items in set E
n(E) = 6

Divide the two values to find the probability of selecting a prime
P(E) = probability of event E happening (ie, getting a prime)
P(E) = n(E)/n(S)
P(E) = 6/15
P(E) = 2/5

The answer as a fraction is 2/5
In decimal form, the answer is 0.4
In percent form, the answer is 40%