Binomial Domestic
1. **Problem Statement:** We are given that 40% of all murders are domestic homicides, and a study selects 10 murder cases. We want to find the probability that between 1 and 3 of these cases are domestic homicides.
2. **Identify the distribution:** This is a binomial probability problem where:
- Number of trials $n = 10$
- Probability of success (domestic homicide) $p = 0.4$
- We want $P(1 \leq X \leq 3)$ where $X$ is the number of domestic homicides.
3. **Binomial probability formula:**
$$
P(X = k) = \binom{n}{k} p^k (1-p)^{n-k}
$$
where $\binom{n}{k}$ is the binomial coefficient.
4. **Using the binomial probability table:** We look up the probabilities for $X=1$, $X=2$, and $X=3$ and sum them:
$$
P(1 \leq X \leq 3) = P(X=1) + P(X=2) + P(X=3)
$$
5. **Calculate each term:**
- $P(X=1) = \binom{10}{1} (0.4)^1 (0.6)^9 = 10 \times 0.4 \times 0.6^9$
- $P(X=2) = \binom{10}{2} (0.4)^2 (0.6)^8 = 45 \times 0.16 \times 0.6^8$
- $P(X=3) = \binom{10}{3} (0.4)^3 (0.6)^7 = 120 \times 0.064 \times 0.6^7$
6. **Evaluate powers:**
- $0.6^9 \approx 0.0101$
- $0.6^8 \approx 0.0168$
- $0.6^7 \approx 0.02799$
7. **Calculate probabilities:**
- $P(X=1) \approx 10 \times 0.4 \times 0.0101 = 0.0404$
- $P(X=2) \approx 45 \times 0.16 \times 0.0168 = 0.12096$
- $P(X=3) \approx 120 \times 0.064 \times 0.02799 = 0.2150$
8. **Sum the probabilities:**
$$
P(1 \leq X \leq 3) \approx 0.0404 + 0.12096 + 0.2150 = 0.37636
$$
**Final answer:** The probability that between 1 and 3 of the cases are domestic homicides is approximately **0.376**.