Jody flips a fair coin three times and each time it lands on heads. Jody believes he can calculate the probability of this occurring by adding the probability of getting a head on each individual flip. Explain why this is incorrect.

When you have multiple events (here each flip of the coin is a individual event) the probability of all the events (or the joint probability) is equal to the product of the probabilities of each event.

For example, with a fair coin the probability of getting heads is 0.50

If you get heads 3 times, and you add the probabilities you get:

0-50*3 = 1.50

this has no sense, because the probability must be a number between 0 and 1.

The actual probability is:

P = 0.50*050*0.50 = 0.125