Question 117457
The total number of balls available is 10+6+4=20 balls.
The probability of choosing a blue ball is 10/20.
The probability of choosing a red ball is 6/20.
The probability of choosing a green ball is 4/20.
P(green or not green) = 1, since the ball I choose must be either green or not green.
P(green) + P(not green) = P(green or not green)
4/20 + P(not green) = 1
P(not green) = 16/20 = 4/5
The answer is B. 
You can eliminate D because none of the probability can sum to 18 out of 20(9/10). The only possible choices are 16/20, 14/20, or 10/20. 
You can also eliminate C because it's not possible to sum to repeating fraction from the possible probabilities (0.5,0.3,0.2).