Probability Complements
1. **Problem 4a:** Find the complement probability $P(A^c)$ given $P(A) = 0.0175$.
The complement rule states:
$$P(A^c) = 1 - P(A)$$
Calculate:
$$P(A^c) = 1 - 0.0175 = 0.9825$$
2. **Problem 4b:** Given 61% believe life exists elsewhere, find the probability someone does *not* believe.
Using complement rule:
$$P(\text{not believe}) = 1 - 0.61 = 0.39$$
3. **Problem 5:** Find probability of selecting a pea with a green pod or a white flower.
From Table 3-2:
- Green pod with purple flower: 5
- Green pod with white flower: 3
- Yellow pod with white flower: 2
Total peas = 5 + 3 + 4 + 2 = 14
Number with green pod = 5 + 3 = 8
Number with white flower = 3 + 2 = 5
Use formula for union:
$$P(\text{green pod} \cup \text{white flower}) = P(\text{green pod}) + P(\text{white flower}) - P(\text{green pod} \cap \text{white flower})$$
Calculate probabilities:
$$P(\text{green pod}) = \frac{8}{14}$$
$$P(\text{white flower}) = \frac{5}{14}$$
$$P(\text{green pod} \cap \text{white flower}) = \frac{3}{14}$$
So:
$$P = \frac{8}{14} + \frac{5}{14} - \frac{3}{14} = \frac{10}{14} = \frac{5}{7} \approx 0.7143$$
4. **Problem 6:** Find probability of selecting a pea with a yellow pod or a purple flower.
From Table 3-2:
- Yellow pod with purple flower: 4
- Green pod with purple flower: 5
Number with yellow pod = 4 + 2 = 6
Number with purple flower = 5 + 4 = 9
Intersection (yellow pod and purple flower) = 4
Calculate probabilities:
$$P(\text{yellow pod}) = \frac{6}{14}$$
$$P(\text{purple flower}) = \frac{9}{14}$$
$$P(\text{yellow pod} \cap \text{purple flower}) = \frac{4}{14}$$
Use union formula:
$$P = \frac{6}{14} + \frac{9}{14} - \frac{4}{14} = \frac{11}{14} \approx 0.7857$$
5. **Problem 7:** Probability birthday is *not* October 18.
There are 365 days in a year (ignoring leap years).
Probability birthday is October 18:
$$P = \frac{1}{365}$$
Probability birthday is not October 18:
$$P = 1 - \frac{1}{365} = \frac{364}{365} \approx 0.9973$$
6. **Problem 8:** Probability birthday is *not* in October.
October has 31 days.
Probability birthday in October:
$$P = \frac{31}{365}$$
Probability birthday not in October:
$$P = 1 - \frac{31}{365} = \frac{334}{365} \approx 0.9151$$