When calculating probability, we are comparing the number of favorable outcomes to the number of possible outcomes. To calculate the probability that at least 2 fair coins land heads up when 3 are flipped, we will divide the number of favorable outcomes by the number of possible outcomes.
P=Favorable Outcomes/Possible Outcomes
First, we will find the number of possible and favorable outcomes. To do so, we will use the organized list from the exercise. Let's take a look.
Sample Space
HHH
HHT
HT H
HTT
T HH
THT
TTH
TTT
We highlighted the favorable outcomes. Finally, we can find probability. We can see that there are 8 total outcomes in the sample space and 4 of them are favorable. Let's substitute these numbers into the formula.
P(At least2 heads)=4/8=1/2
