The urn contains 5 white, 4 green and 3 red balls. Draw one ball at random, find the probability that it is either not green or blue.

To solve this problem, you must use the formula for the classical definition of probability:

P (A) = m / n,

Where P (A) is the probability of the event A of interest to us, that is, the extraction of a ball of a certain color, m is the number of outcomes favorable to the event, n is the number of all equally possible outcomes of the test. Let’s define the value of n:

n = 5 + 4 + 3 = 12;

1) In order to determine the probability that the removed ball is not green, we determine the number of non-green balls in the urn:

m = 5 + 3 = 8.

Then:

P (A) = 8/12 = 0.667.

2) In order to determine the probability that the removed ball is not blue, we determine the number of non-blue balls in the urn:

m = 5 + 4 + 3 = 12.

Then:

P (A) = 12/12 = 1.