How to Calculate Normal Probability

Normal probability calculates the number of occurrences for an event based on a certain number of possible outcomes. The calculation is generally expressed as a percentage or a number from zero to one. Single event probability is the most common calculation. Specifically, it is used to find the probability of a single event. For instance, a coin toss is a single event with two possible outcomes: heads or tails.

Things You'll Need

• Calculator or spreadsheet software

Instructions

1. Review probability formula. The probability that event X occurs is P(X) = n(X) / n(Y) where n(X) equals number of times an event occurs and n(Y) equals the number of possible outcomes.

2. Define variables and work through an example. A die has six outcomes. For an example, calculate the probability of getting odd numbers. In this example, the number of odd numbers is three and the number of possible outcomes is six.

3. Substitute the variables into the formula. N(X) = 3 which is the total number of odd numbers occurring. N(Y) = 6 which is the total number of outcomes. The formula is P(X) = n(X) / n(Y) = 3 / 6 = 0.5.

4. Interpret the answer. The answer is .5 which means that the probability of rolling an odd number on a die is .5 or 50 percent.

References

• Normal Probability Function and Calcultor

Resources

• Probability Calculator