Probability & Permutation

Factorial notation

It is a simple way of writing the product of all whole numbers up to a given number.

-The n factorial is defined as the product of the integers from 1 to n.

-It can be written as "n!". This means that we are looking for (n)(n-1)(n-2)(n-3)...(3)(2)(1)

N.B: Two numbers containing factorials and being divided by one another does not mean they can be simplified: 10!/5!=/=2!

Permutation ( Ordered Arrangement)

It is the ordering of a set of objects.

Using factorial notation: n objects can be arranged in "n!" ways.

Theorem for number of permutations (with no repetitions):


When there is repetition, it is possible to assign different "n"s for each.This results in a new formula:


Free Math Lessons Permutations and Probability


It is a measure or estimation of how likely it is that something will happen.

The sample space is the set of all possible outcomes of the experiment.The Event (E) is a subset of the sample space.

P(E)=r/n where r is the number of ways for a specific outcome and n is the number of all outcomes. This is to determine the success of an event or its occurrence.

To determine non-occurrence: P(E/)= 1-r/n

The sum of the probabilities in any experiment is equal to 1.

the probability of an even ranges between 0 and 1. if the event's occurrence is impossible, then the probability is 0, although absolute certainty means that the probability is 1.

Probability 101