A bag contains 20 marbles of the same size that are blue, green, and red. The probability of picking a blue marble is 20%. The probability of picking a green marble is 50%. Determine the probability of picking a red marble from the bag and then classify the probability of picking a red marble as likely or not likely to occur.

There are only three colours.

By Kolmogorov's second axiom, the sum of probabilities of all possible outcomes is one, which means that

P (blue) + P (green) + P (red) = 1

We know that

P (blue) = 0.20

P (green) = 0.50

so above equation reduces to

0.20+0.50+P (red) = 1

Solve for P (red) = 1 - 0.20 - 0.50 = 0.30.

If we define likely as over 50%, then it's not likely.