1. **State the problem:** We want to find the probability that exactly 16 out of 250 workers use public transportation, given that 5% of workers use it.
2. **Identify the distribution:** The number of workers using public transportation, $X$, follows a binomial distribution with parameters $n=250$ and $p=0.05$.
3. **Use normal approximation:** For large $n$, the binomial distribution can be approximated by a normal distribution with mean $\mu = np$ and variance $\sigma^2 = np(1-p)$.
Calculate mean and standard deviation:
$$\mu = 250 \times 0.05 = 12.5$$
$$\sigma = \sqrt{250 \times 0.05 \times 0.95} = \sqrt{11.875} \approx 3.447$$
4. **Apply continuity correction:** To find $P(X=16)$, approximate $P(15.5 < X < 16.5)$ using the normal distribution.
5. **Convert to standard normal variable $Z$:**
$$Z = \frac{X - \mu}{\sigma}$$
Calculate:
$$Z_1 = \frac{15.5 - 12.5}{3.447} \approx 0.87$$
$$Z_2 = \frac{16.5 - 12.5}{3.447} \approx 1.16$$
6. **Find probabilities from standard normal table:**
$$P(15.5 < X < 16.5) \approx P(0.87 < Z < 1.16) = P(Z < 1.16) - P(Z < 0.87)$$
Using standard normal CDF values:
$$P(Z < 1.16) \approx 0.8770$$
$$P(Z < 0.87) \approx 0.8078$$
7. **Calculate final probability:**
$$P(X=16) \approx 0.8770 - 0.8078 = 0.0692$$
**Answer:** The probability that exactly 16 workers use public transportation is approximately **0.0692**.
Normal Approximation 204Ef6
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