X	20	30	40	50
P(X=x)	1.1	0.6	.2	.1

1. Yes, the probabilities add to 1 and they are all positive.
2. Yes, the probabilities are all positive.
3. No, the values of X are too far apart and the probabilities add up to a value greater than 1.
4. No, while the probabilities are all positive, the P(X=20)=1.1. Probabilities cannot exceed 1.