Probability

Question

Carrie McCallister flips a coin twice and gets heads both times. What is the probability that Carrie will get tails the third time she flips the coin?

Answer 1

Every time Carrie flips the coin there is a 50% chance of heads and a 50% chance of tails, regardless of previous outcomes. So, the probability that Carrie will flip and get tails is 50%.

 

Note: The answer is different if the questions asks, what is the probability that Carrie will flip a coin three times and get the sequence H-H-T. This particular sequence has a 1/8 chance of happening, which can be determined two ways:

 

H-H-T = (1/2)*(1/2)*(1/2) (multiply the probability of each independent event to get probability of sequence

 

OR

 

List your possibilities (not useful when you get into larger sets)

 

H-H-H

H-H-T

H-T-H

H-T-T

T-H-H

T-H-T

T-T-H

T-T-T

 

Since there are 8 possible outcomes, and the likeliness of each one is equal, this outcome would be 1/8

Answer 2

flipping a coin twice and getting heads both times has no affect on future flips of the coin

the probability that Carrie will get tails on the third flip is 1/2