Probabilities Combined
1. **Problem 02: Two cards drawn with replacement**
We want conditional probabilities about the second card given the first card.
(a) Probability second card is a face card given first card was red:
- Total cards in deck: 52.
- Red cards: 26
- Face cards: Jack, Queen, King in each suit = 12 total (3 per suit * 4 suits).
- Red face cards: Jack, Queen, King of hearts and diamonds = 6.
Since the draw is with replacement, the second card distribution is the same as a fresh draw.
$$P(\text{Face card}) = \frac{12}{52} = \frac{3}{13}$$
This is independent of first card being red.
$$\Rightarrow P(\text{Second card face} | \text{First card red}) = P(\text{Face card}) = \frac{3}{13}$$
(b) Probability second card is an ace given first was face card:
- Number of face cards: 12
- Number of aces: 4
- Since with replacement, second card is independent.
So:
$$P(\text{Second card ace} | \text{First card face}) = P(\text{Ace}) = \frac{4}{52} = \frac{1}{13}$$
(c) Probability second card is a black jack given first card was a red ace:
- Red aces: 2 (hearts and diamonds).
- Black jack cards: Jack of spades and Jack of clubs = 2.
Again, independent draws:
$$P(\text{Black Jack}) = \frac{2}{52} = \frac{1}{26}$$
2. **Problem 03: Prison escape attempts**
Given counts for each season and category, probabilities are counted by dividing category frequency by 45 (total years).
(a) Probability escapes between 16 and 20 during winter:
Count from table for winter in 16–20 row: 3
$$P = \frac{3}{45} = \frac{1}{15}$$
(b) Probability more than 10 escapes in summer:
More than 10 means categories 11–15, 16–20, 21–25, More than 25
Sum counts for summer:
11–15: 7, 16–20: 6, 21–25: 5, More than 25: 4
Total = 7 + 6 + 5 + 4 = 22
$$P = \frac{22}{45}$$
(c) Probability escapes between 11 and 20 inclusive in any season:
Combine categories 11–15 and 16–20 for each season, sum counts and divide by total possible counts (45*4=180)
- Winter: 5+3 = 8
- Spring: 8+4 = 12
- Summer: 7+6 = 13
- Fall: 7+5 = 12
Sum = 8 + 12 + 13 + 12 = 45
$$P = \frac{45}{180} = \frac{1}{4}$$
3. **Problem 04: Education survey**
Total respondents: 1000
(a) Undergraduate (U):
$$P(U) = \frac{300}{1000} = 0.3$$
(b) Graduate (G):
$$P(G) = \frac{700}{1000} = 0.7$$
(c) Female (F):
$$P(F) = \frac{400}{1000} = 0.4$$
(d) Male-Graduate (MG):
Number male graduate = 450
$$P(MG) = \frac{450}{1000} = 0.45$$
(e) Undergraduate-Female (UF):
Number undergraduate female = 150
$$P(UF) = \frac{150}{1000} = 0.15$$
(f) Probability randomly selected female is graduate:
Using conditional probability:
$$P(G|F) = \frac{P(G \cap F)}{P(F)} = \frac{250/1000}{400/1000} = \frac{250}{400} = 0.625$$
(g) Probability randomly selected undergraduate is male:
$$P(M|U) = \frac{P(M \cap U)}{P(U)} = \frac{150/1000}{300/1000} = \frac{150}{300} = 0.5$$
4. **Problem 05: Boxes of bananas fruit damage**
Total boxes: 10,000
Damaged fruit:
Ecuadoran: 200
Honduran: 365
Total damaged = 200 + 365 = 565
Overripe fruit:
Ecuadoran: 840
Honduran: 295
Total overripe = 840 + 295 = 1,135
(a) Probability box chosen at random contains damaged fruit:
$$P(D) = \frac{565}{10000} = 0.0565$$
Probability box chosen contains overripe fruit:
$$P(O) = \frac{1135}{10000} = 0.1135$$
(b) Probability randomly selected box is from Ecuador or Honduras:
Since these are the only two origins,
$$P(\text{Ecuador}) = \frac{6000}{10000} = 0.6$$
$$P(\text{Honduras}) = 0.4$$
Sum is 1.
(c) Probability box came from Honduras given overripe fruit:
Using conditional probability:
$$P(H|O) = \frac{P(H \cap O)}{P(O)} = \frac{295/10000}{1135/10000} = \frac{295}{1135} \approx 0.260"$$
(d) If damaged and overripe are mutually exclusive:
$$P(D \cup O) = P(D) + P(O) = 0.0565 + 0.1135 = 0.17$$
If NOT mutually exclusive, assuming overlap is zero (not given data), use the formula:
$$P(D \cup O) = P(D) + P(O) - P(D \cap O)$$
Since $P(D \cap O)$ unknown, cannot numerically calculate.
**Final answers:**
- Problem 02: (a) $\frac{3}{13}$, (b) $\frac{1}{13}$, (c) $\frac{1}{26}$
- Problem 03: (a) $\frac{1}{15}$, (b) $\frac{22}{45}$, (c) $\frac{1}{4}$
- Problem 04: (a) 0.3, (b) 0.7, (c) 0.4, (d) 0.45, (e) 0.15, (f) 0.625, (g) 0.5
- Problem 05: (a) $P(D)=0.0565$, $P(O)=0.1135$, (b) 0.6 and 0.4, (c) $\approx$0.26, (d) mutually exclusive $P(D\cup O)=0.17$, otherwise unknown.