Question

a marble is randomly drawn from a ba
that with 5 blue marbles, 8 red marble
and 7 green marbles.
event a: red
event b: blue
p(a or b) = ?

Explanation:

Step1: Calculate total marbles

Total marbles = 5 + 8 + 7 = 20

Step2: Check mutual exclusivity

Event A (red) and B (blue) can't occur together, so $P(A \text{ and } B) = 0$

Step3: Compute $P(A \text{ or } B)$

$P(A) = \frac{8}{20}$, $P(B) = \frac{5}{20}$. Use $P(A \cup B) = P(A) + P(B) - P(A \cap B)$
$P(A \cup B) = \frac{8}{20} + \frac{5}{20} - 0 = \frac{13}{20}$

Answer:

$\frac{13}{20}$