Given that a random variable X follows a normal distribution with a mean \( \mu = 15 \) and variance \( \sigma^2 = 25 \), find the standard deviation.

Step 1 ：The standard deviation of a normal distribution is calculated as the square root of the variance, which is represented as \( \sigma \).

Step 2 ：Given the variance \( \sigma^2 = 25 \), we can calculate the standard deviation as \( \sigma = \sqrt{\sigma^2} \).

Step 3 ：Substituting the given variance into the equation, we get \( \sigma = \sqrt{25} \).