If s = 8 and n = 25, what is the standard error of the mean?

• A. 8/√25
• B. 8/25
• C. √(8^2 + 25^2)
• D. 25/8

Answer: (A)

The standard error of the mean tells you how much the sample average is expected to vary from one sample to another, assuming you know the variability within observations. It’s computed as the sample standard deviation divided by the square root of the sample size: SEM = s / √n. With s = 8 and n = 25, the SEM is 8 / √25 = 8 / 5 = 1.6. This shows that as you collect more data, the precision of the mean estimate improves by a factor of √n. The option that matches this formula is 8/√25, which gives 1.6. The other expressions don’t reflect this standard relationship: dividing by 25 uses the full n rather than its square root, combining squares isn’t the right approach here, and 25/8 is the reciprocal of the correct scaling.