Explanation

Step 1: Convert percentages to decimals Returns: 0.21, 0.17, 0.11, 0.18, 0.15

Step 2: Calculate sample mean $\bar{x} = \frac{0.21 + 0.17 + 0.11 + 0.18 + 0.15}{5} = \frac{0.82}{5} = 0.164$

Step 3: Calculate sum of squared deviations $\sum (x_i - \bar{x})^2 = (0.21-0.164)^2 + (0.17-0.164)^2 + (0.11-0.164)^2 + (0.18-0.164)^2 + (0.15-0.164)^2$ $= (0.046)^2 + (0.006)^2 + (-0.054)^2 + (0.016)^2 + (-0.014)^2$ $= 0.002116 + 0.000036 + 0.002916 + 0.000256 + 0.000196$ $= 0.00552$

Step 4: Calculate unbiased sample variance $s^2 = \frac{\sum (x_i - \bar{x})^2}{n-1} = \frac{0.00552}{4} = 0.00138$

Therefore, the correct unbiased sample variance is 0.00138.