Applet about general introduction to probability
Here is an applet link about a virtual coin toss:
Toss Virtual Coins
This applet allows the user to select the probability of heads and the number of tosses. By clicking the "TOSS" button, the applet shows the process of tossing coins virtually and calculates the probability of tossing a head. By clicking the "Show true probability" button, users can compare the probability of tossing a head that users get and the actual probability. Also, the site provides some tests in the "Quiz Me" section to help users understand the definition of probability better.
Author: Statistical Applets.
Addition Rule
The addition rule is used to determine the probability of at least one of two (or more) events occurring. In general, the probability of either event A or B is given by:
P(A or B) = P(A) + P(B) - P(A and B)
If A and B are mutually exclusive, this means they cannot occur together, i.e. P(A and B)=0. Therefore, for mutually exclusive events the probability of either A or B occurring is given by:
P(A or B) = P(A) + P(B)