Consider the probability that fewer than 20 out of 155 people have been in a car accident. Assume the probability that a given person has been in a car accident is 10%. Approximate the probability using the normal distribution. Round your answer to four decimal places.

0.8264 = 82.64% probability that fewer than 20 out of 155 people have been in a car accident.

Step-by-step explanation:

Binomial probability distribution

Probability of exactly x sucesses on n repeated trials, with p probability.

Can be approximated to a normal distribution, using the expected value and the standard deviation.

The expected value of the binomial distribution is:

The standard deviation of the binomial distribution is:

Normal probability distribution

Problems of normally distributed samples can be solved using the z-score formula.

In a set with mean and standard deviation , the zscore of a measure X is given by:

The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the pvalue, we get the probability that the value of the measure is greater than X.

When we are approximating a binomial distribution to a normal one, we have that , .

In this problem, we have that:

So

Consider the probability that fewer than 20 out of 155 people have been in a car accident.

The number of people that have been in a car acident is a discrete value, so fewer than 20 is 19 or less.

This probability is the pvalue of Z when X = 19.

has a pvalue of 0.8264

0.8264 = 82.64% probability that fewer than 20 out of 155 people have been in a car accident.

ca = ec

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