Answer:
2/3
Explanation:
There are 4 red balls and 8 yellow balls. 
Therefore, there are total 12 balls in the bag. 
n(S) = 12
Let A be the event when the ball drawn is not a red ball. 
The balls which are not red will be yellow balls and there are 8 yellow balls so, 
n(A) = 8
Probability that the ball drawn randomly from the bag is not a red ball,
p(A) = n(A) / n(S)
 = 8/12
 = 2/3
Therefore, the probability of the ball drawn randomly is not a red ball is 2/3.