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According to the Centers of Disease Control and Prevention, \(52 \%\) of U.S. households had no landline and only had cell phone service. Suppose a random sample of 40 U.S. households is taken. a. Find the probability that exactly 20 the households sampled only have cell phone service. b. Find the probability that fewer than 20 households only have cell phone service. c. Find the probability that at most 20 households only have cell phone service. d. Find the probability that between 20 and 23 households only have cell phone service.

Short Answer

Expert verified
The answer will be the calculated values from step 2 (Part a), step 4 (Part b), step 6 (Part c) and step 8 (Part d).

Step by step solution

01

Setting up formula for Part a

Here we're asked to find the probability that exactly 20 households only have cell phone service. This corresponds to a binomial probability \(P(20; 40, 0.52)\). Thus we can apply the binomial formula to compute this probability.
02

Applying formula for Part a

Applying the binomial probability formula, we get \(P(20; 40, 0.52) = \binom{40}{20} (0.52)^{20} (1-0.52)^{40-20}\). Calculate this expression to get the value of the probability.
03

Setting up formula for Part b

Here we're asked to find the probability that fewer than 20 households have only cell phone service. This corresponds to the sum of binomial probabilities from x=0 to 19: \(\Sigma_{x=0}^{19} P(x;40,0.52)\).
04

Applying formula for Part b

To get this probability, we have to calculate and sum up 20 binomial probabilities, that is, \(P(x;40,0.52)\) for x from 0 to 19.
05

Setting up formula for Part c

Now we need to find the probability that at most 20 households only have cell phone service. This corresponds to the sum of binomial probabilities from x=0 to 20 which is similar to Part b but includes 20 as well. It can be represented as: \(\Sigma_{x=0}^{20} P(x;40,0.52)\).
06

Applying formula for Part c

Calculate and sum up 21 binomial probabilities, i.e., \(P(x;40,0.52)\) for x from 0 to 20 to get the result.
07

Setting up formula for Part d

We're asked to find the probability that between 20 and 23 households only have cell phone service. This corresponds to the sum of binomial probabilities from x=20 to 23, represented as: \(\Sigma_{x=20}^{23} P(x;40,0.52)\).
08

Applying formula for Part d

Calculate and sum up 4 binomial probabilities, i.e., \(P(x;40,0.52)\) for x from 20 to 23 to get the probability.

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