Share Standard Deviation
1. **State the problem:** We are given probabilities and returns for shares and asked to find the standard deviation of the share returns given the expected return is 23.25%.
2. **List the data:**
- Probabilities: $p = [0.15, 0.2, 0.3, 0.25, 0.1]$
- Returns: $r = [0.05, 0.20, 0.40, 0.20, 0.15]$
- Expected return: $E(R) = 0.2325$
3. **Recall the formula for variance:**
$$\sigma^2 = \sum p_i (r_i - E(R))^2$$
4. **Calculate each squared deviation:**
- $(0.05 - 0.2325)^2 = 0.03330625$
- $(0.20 - 0.2325)^2 = 0.00105625$
- $(0.40 - 0.2325)^2 = 0.02830625$
- $(0.20 - 0.2325)^2 = 0.00105625$
- $(0.15 - 0.2325)^2 = 0.00680625$
5. **Multiply each squared deviation by its probability:**
- $0.15 \times 0.03330625 = 0.00499594$
- $0.2 \times 0.00105625 = 0.00021125$
- $0.3 \times 0.02830625 = 0.00849188$
- $0.25 \times 0.00105625 = 0.00026406$
- $0.1 \times 0.00680625 = 0.00068063$
6. **Sum these values to get variance:**
$$\sigma^2 = 0.00499594 + 0.00021125 + 0.00849188 + 0.00026406 + 0.00068063 = 0.01464376$$
7. **Calculate standard deviation:**
$$\sigma = \sqrt{0.01464376} = 0.121\approx 12.1\%$$
8. **Compare with given options:** The closest option is 12.02%.
**Final answer:** The standard deviation of the share returns is approximately **12.02%**.