Math Is Fun
Math Is Fun: Probability Line
A good explanation of the probability of events, using probability lines in the examples.
Interactive Mathematics
Interactive Mathematics: Counting and Probability
An introduction to the concept of counting and probability includes working with factorials and finding the probability of an event.
Shmoop University
Shmoop: Basic Statistics & Probability: Factorials
The probability resource investigates factorials. Students learn about the topic through notes and examples. The tutorial consists of practice exercises to check for comprehension of the concept.
That Quiz
That Quiz: Probabilidad
Test your knowledge of probability by taking this practice test. Five levels are provided and it also tracks the number of correct and wrong answers.