1. **Problem statement:** We want to find the probability that a binomial random variable $X$ with parameters $n=10$ and $p=0.3$ takes the value 3, i.e., $P(X=3)$.
2. **Formula:** The probability mass function of a binomial distribution is given by:
$$P(X=k) = \binom{n}{k} p^k (1-p)^{n-k}$$
where $\binom{n}{k} = \frac{n!}{k!(n-k)!}$ is the binomial coefficient.
3. **Apply the formula:**
$$P(X=3) = \binom{10}{3} (0.3)^3 (0.7)^7$$
4. **Calculate the binomial coefficient:**
$$\binom{10}{3} = \frac{10!}{3!7!} = \frac{10 \times 9 \times 8}{3 \times 2 \times 1} = 120$$
5. **Calculate powers:**
$$(0.3)^3 = 0.027$$
$$(0.7)^7 \approx 0.0823543$$
6. **Multiply all parts:**
$$P(X=3) = 120 \times 0.027 \times 0.0823543 \approx 0.2679$$
7. **Interpretation:** The probability $P(X=3)$ is approximately 0.27.
**Final answer:** D) 0.27
Binomial Probability 449C24
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