If an unbiased die is thrown, what is the probability that it will show a 3 or an even number?
So, a normal die has 6 sides, unless the question is referring to another type of die (e.g. 8 sided).
In a 6-sided die, there are four numbers that fits the requirements: 2,3,4, and 6. Given that there are 4 possibilities and 6 total outcomes, you just divide those to numbers to get
The possibilities are each of the six sides.
What we're interested in is
That's four out of the six possible numbers the die can land on, so your answer for probability is
which can be simplified into
Let X=number on the die.
Since the die is unbiased, we can use the classical approach in assigning the probabilities.
P(X=2 U X=4 U X=6)=
Since the problem is an 'or' statement (meaning union) then,
P(X=3 U X=2 U X=4 U X=6) = P(X=3)+P(X=2 U X=4 U X=6) =