An unbiased die is tossed. Find the probability of getting a multiple of 3.

Concept: For an experiment with equally likely outcomes, such as a single toss of a fair (unbiased) die, the classical probability of an event is the ratio of the number of favourable outcomes to the total number of possible outcomes: P(event) = (Number of favourable outcomes) / (Total number of possible outcomes).

Application:

1. The sample space for one toss of an unbiased die is {1, 2, 3, 4, 5, 6}, so the total number of possible outcomes is 6.

2. Among these six outcomes, the values that are multiples of 3 are 3 and 6, so the number of favourable outcomes is 2.

3. Applying the classical probability formula: P(multiple of 3) = 2/6 = 1/3.

Cross-check: Considering the complementary event, the outcomes that are not multiples of 3 are {1, 2, 4, 5}, four outcomes out of six, giving a probability of 4/6 = 2/3. Since 1 minus 2/3 equals 1/3, this matches the result obtained above.