Normal Probabilities
1. Problem Statement:
We have two normal distributions:
- $X \sim \mathcal{N}(44, 2^2)$ means $X$ is normally distributed with mean $\mu=44$ and standard deviation $\sigma=2$.
- $X \sim \mathcal{N}(66, 11^2)$ means $X$ is normally distributed with mean $\mu=66$ and standard deviation $\sigma=11$.
We need to calculate probabilities from these distributions rounded to 3 decimal places.
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### First distribution: $X \sim \mathcal{N}(44,4)$
2. Calculate $P(X \leq 47.2)$:
- Compute z-score: $z = \frac{47.2 - 44}{2} = \frac{3.2}{2} = 1.6$
- From standard normal tables or calculator, $P(Z \leq 1.6) = 0.9452$
- So, $P(X \leq 47.2) = 0.945$
3. Calculate $P(X > 44.8)$:
- $z = \frac{44.8 - 44}{2} = 0.4$
- $P(Z > 0.4) = 1 - P(Z \leq 0.4) = 1 - 0.6554 = 0.3446$
- So, $P(X > 44.8) = 0.345$
4. Calculate $P(X > 41.6)$:
- $z = \frac{41.6 - 44}{2} = -1.2$
- $P(Z > -1.2) = 1 - P(Z \leq -1.2) = 1 - 0.1151 = 0.8849$
- So, $P(X > 41.6) = 0.885$
5. Calculate $P(X < 39)$:
- $z = \frac{39 - 44}{2} = -2.5$
- $P(Z < -2.5) = 0.0062$
- So, $P(X < 39) = 0.006$
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### Second distribution: $X \sim \mathcal{N}(66,11^2)$
6. Calculate $P(X \leq 88)$:
- $z = \frac{88 - 66}{11} = 2$
- $P(Z \leq 2) = 0.9772$
- So, $P(X \leq 88) = 0.977$
7. Calculate $P(X \leq 59.4)$:
- $z = \frac{59.4 - 66}{11} = -0.6$
- $P(Z \leq -0.6) = 0.2743$
- So, $P(X \leq 59.4) = 0.274$
8. Calculate $P(X > 51.7)$:
- $z = \frac{51.7 - 66}{11} = -1.3$
- $P(Z > -1.3) = 1 - P(Z \leq -1.3) = 1 - 0.0968 = 0.9032$
- So, $P(X > 51.7) = 0.903$
9. Calculate $P(64.9 < X < 73.7)$:
- $z_1 = \frac{64.9 - 66}{11} = -0.1$
- $z_2 = \frac{73.7 - 66}{11} = 0.7$
- $P(-0.1 < Z < 0.7) = P(Z \leq 0.7) - P(Z \leq -0.1) = 0.7580 - 0.4602 = 0.2978$
- So, $P(64.9 < X < 73.7) = 0.298$
Final Answers:
- $P(X \leq 47.2) = 0.945$
- $P(X > 44.8) = 0.345$
- $P(X > 41.6) = 0.885$
- $P(X < 39) = 0.006$
- $P(X \leq 88) = 0.977$
- $P(X \leq 59.4) = 0.274$
- $P(X > 51.7) = 0.903$
- $P(64.9 < X < 73.7) = 0.298$