The question asks for the probability that a marble is NOT YELLOW
Total Marbles: orange+yellow+blue=7+3+2=12
We need to count all marbles except yellow:
orange+blue=7+2=9
Now to find the probability that is NOT YELLOW:
= 
Answer is 3/4
Hope it helps!
The answer is true. A conditional probability is a measure
of the probability of an event given that (by assumption, presumption,
assertion or evidence) another event has occurred. If the event of interest is
A and the event B is known or assumed to have occurred, "the conditional
probability of A given B", or "the probability of A in the condition
B", is usually written as P (A|B). The conditional probability of A given
B is well-defined as the quotient of the probability of the joint of events A
and B, and the probability of B.
