Question

Kevin rolls a 6 sided die what is the probability that he gets a number greater than 3 or a prime number

Answer 1

Let event A be the probability of getting a number greater than 3.
P(A) = 3/6
Let B be the probability of getting a prime number.
P(B) = 3/6
However 5 is common to both events.
$P(A\cap B)=\frac{1}{6}$
A union B is the event A or B.
$P(A\cup B)=P(A)+P(B)-P(A\cap B)$
$P(A\cup B)=\frac{3}{6}+\frac{3}{6}-\frac{1}{6}=\frac{5}{6}$
Therefore the probability that he gets a number greater than 3 or a prime number is 5/6.