Hi,thank you for posting your question here at Brainly.
Probability is a numerical value that represents a fraction of a whole. Since there are 4 samples indicated in row X, then there must be 4 probabilities corresponding to each. The sum of all those probabilities must equal to 1. With this information, we could already find the missing probability.
Summation of P = 1 = 0.40 + 0.20 + 0.20 + x
x = 1 - 0.4 - 0.2 - 0.2
x = 0.2 <-- missing probability
