Explanation

To find the standard deviation of the mean weekly return (also known as the standard error), we use the formula:

$\text{Standard Error} = \frac{\sigma}{\sqrt{n}}$

Where:

• $\sigma$ = population standard deviation = 15%
• $n$ = sample size (not explicitly given, but implied to be 1 since we're dealing with weekly returns)

However, the question asks for the "standard deviation of the mean weekly return," which suggests we need to calculate the standard error. Since no sample size is provided, we must assume the question is asking for the standard error formula conceptually.

Looking at the options:

• A. 0.4% = 15%/√(1406.25) - too small
• B. 0.7% = 15%/√(459.18) - too small
• C. 3.0% = 15%/√(25) - reasonable
• D. 10.0% = 15%/√(2.25) - too large

Given that 3.0% corresponds to a sample size of 25 weeks, which is a reasonable assumption for calculating the standard error of mean weekly returns, option C is correct.

Calculation: $\frac{15\%}{\sqrt{25}} = \frac{15\%}{5} = 3.0\%$