Based on data from the national center of health, 26% of adults are overweight. A random sample of 15 adults is taken. Calculate the probability that three of four of 15 people selected are overweight?

## Calculating three or four of 15 adults

# 1 Answer

This is an example of a binomial event and probability distribution. For each person you select, they are either overweight or not-only two possible outcomes. If we define 'success' as selecting an overweight person, the probability of success when we select someone is denoted p, and is given as 26%, or, in decimal form, .26.

p=.26 <-- probability of success

q=1-.26=.74 <-- probability of 'failure', choosing someone who is not overweight. p+q=1

n=15 <-- Number of people we are selecting

We need to add the probabilities of getting exactly 3 out of 15 and getting exactly 4 out of 15. We'll use x to represent the number of successes in our selection of 15 adults:

Our expression of the total probability of selecting either 3 or 4 people out of 15: P(x=3) + P(x=4)

The binomial probability formula: P(X=x) = _{n}C_{x }* p^{x
}* q^{n-x}

_{n}C_{x} is our notation for a combination, which mathematically equals [ n! / ( x! * (n-x)! ) ]

The probability of picking 3 or four people out of 15 is the sum of the following two expressions:

P(X=3) = _{15}C_{3} * (0.26)^{3} * (0.74)^{15-3} = 455 * (0.26)^{3} * (0.74)^{12} = 0.216

P(X=4) = _{15}C_{4} * (0.26)^{4} * (0.74)^{15-4} = 1365 * (0.26)^{4} * (0.74)^{11} = 0.227

P(X=3) + P(X=4) = 0.216 + 0.227 = 0.443

The probability of selecting three or four overweight people in a random sample of 15 is 0.443.