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# Not sure what to do to show my work for this probability question?

Update:

In a recent survey, only 47% of Americans had a three-day supply of bottled water in case of emergency. Suppose a sample of 35 Americans is selected at random.

a. What is the probability that exactly 12 Americans have a three-day supply of bottled water on hand?

b. What is the probability that at least 18 Americans have a three-day supply of bottled water on hand?

### 1 Answer

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- PuzzlingLv 710 months agoFavorite Answer
Use the binomial probability formula.

P(X = k) = C(n, k) * p^k * q^(n - k)

n : number of trials (35)

k : number of successes (12)

p : probability of success (0.47)

q : probability of failure (1-p = 0.53)

Example:

P(X = 12) = C(35, 12) * 0.47^12 * 0.53^23

As for at least 18, you'd want to calculate the probability of 18 and above.

P(X = 18) = 0.116755

P(X > 18) = 0.243480

P(X ≥ 18) = 0.360135

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