Probability is the mathematical measure of how likely an event is to happen, expressed as a fraction between 0 (impossible) and 1 (certain).

The Simple Formula

Probability = (Number of Desired Outcomes) / (Total Number of Possible Outcomes)

1. Flipping a Coin

A coin has 2 sides (Heads and Tails). The probability of landing on Heads is 1/2 (50%).

2. Rolling a Standard 6-Sided Die

  • Probability of rolling a 4: 1/6 (about 16.7%)
  • Probability of rolling an even number (2, 4, 6): 3/6 = 1/2 (50%)
  • Probability of rolling a number greater than 4 (5, 6): 2/6 = 1/3 (33.3%)

Theoretical vs. Experimental Probability

In theory, flipping a coin 10 times should give 5 heads and 5 tails. But if you try it right now, you might get 7 heads and 3 tails! That is experimental probability. The more trials you run, the closer the experimental result gets to the theoretical expectation.