Discrete Probability B3Ce77
1. **Problem Statement:**
A basket contains 10 ripe and 4 unripe bananas. Four bananas are taken one after another. We want to find the possible values of the random variable $R$ representing the number of ripe bananas selected.
2. **Step 1: List the sample space (S)**
The sample space consists of all possible outcomes of selecting 4 bananas from 14 (10 ripe + 4 unripe).
3. **Step 2: Count the number of ripe bananas ($R$) in each outcome**
Possible values of $R$ are $0,1,2,3,4$ since we can select from none to all ripe bananas.
4. **Step 3: Frequency description**
Calculate the number of ways to select $k$ ripe bananas and $4-k$ unripe bananas:
$$\text{Frequency}(R=k) = \binom{10}{k} \times \binom{4}{4-k}$$
for $k=0,1,2,3,4$.
5. **Step 4: Probability description**
Total number of ways to select 4 bananas from 14:
$$\binom{14}{4}$$
Probability for each $k$:
$$P(R=k) = \frac{\binom{10}{k} \times \binom{4}{4-k}}{\binom{14}{4}}$$
6. **Calculate each probability:**
- $P(R=0) = \frac{\binom{10}{0} \binom{4}{4}}{\binom{14}{4}} = \frac{1 \times 1}{1001} = \frac{1}{1001}$
- $P(R=1) = \frac{\binom{10}{1} \binom{4}{3}}{1001} = \frac{10 \times 4}{1001} = \frac{40}{1001}$
- $P(R=2) = \frac{\binom{10}{2} \binom{4}{2}}{1001} = \frac{45 \times 6}{1001} = \frac{270}{1001}$
- $P(R=3) = \frac{\binom{10}{3} \binom{4}{1}}{1001} = \frac{120 \times 4}{1001} = \frac{480}{1001}$
- $P(R=4) = \frac{\binom{10}{4} \binom{4}{0}}{1001} = \frac{210 \times 1}{1001} = \frac{210}{1001}$
7. **Summary Table:**
| Value of $R$ | Frequency | Probability |
|--------------|-----------|-------------|
| 0 | 1 | $\frac{1}{1001}$ |
| 1 | 40 | $\frac{40}{1001}$ |
| 2 | 270 | $\frac{270}{1001}$ |
| 3 | 480 | $\frac{480}{1001}$ |
| 4 | 210 | $\frac{210}{1001}$ |
---
**Homework Problem:**
- Basket: 10 unripe, 4 ripe bananas
- Select 3 bananas
- Find possible values of $U$ = number of unripe bananas selected
This problem is similar; possible values of $U$ are $0,1,2,3$.
Frequency:
$$\text{Frequency}(U=k) = \binom{10}{k} \times \binom{4}{3-k}$$
Probability:
$$P(U=k) = \frac{\binom{10}{k} \times \binom{4}{3-k}}{\binom{14}{3}}$$
This completes the solution for the first problem.