Question:medium

In measuring reaction times, a psychologist estimates that the standard deviation is 0.05 seconds. How large a sample of measurements should be taken in order to be 95% confident that the error of the estimate will not exceed 0.01 seconds?

Show Hint

When calculating sample size, always round the result up to the next integer. Rounding down would result in a sample size that is slightly too small to guarantee the desired margin of error. For 95% confidence, use \(Z=1.96\); sometimes problems will approximate this with \(Z=2\) for simpler calculations, which would have resulted in \(n=100\).
Updated On: Feb 18, 2026
  • \( n \ge 80 \)
  • \( n \ge 72 \)
  • \( n \ge 96 \)
  • \( n \ge 69 \)
Show Solution

The Correct Option is C

Solution and Explanation

Step 1: Concept Explanation:
This problem involves determining the minimum sample size to accurately estimate a population mean (true reaction time) within a given margin of error and confidence level. We assume a large population, negating the need for finite population correction.

Step 2: Core Formula:
The margin of error (E) for estimating a population mean is: \[ E = Z_{\alpha/2} \frac{\sigma}{\sqrt{n}} \] Solve for the sample size, \(n\): \[ n = \left( \frac{Z_{\alpha/2} \sigma}{E} \right)^2 \]
Step 3: Detailed Solution:
Given values: - Confidence Level: 95%, with a Z-value of \(Z_{\alpha/2} = Z_{0.025} = 1.96\). - Population Standard Deviation (\(\sigma\)): Estimated at 0.05 seconds. - Maximum Margin of Error (E): Should not exceed 0.01 seconds, thus \(E = 0.01\). Substitute these values into the sample size formula: \[ n = \left( \frac{1.96 \times 0.05}{0.01} \right)^2 \] \[ n = \left( \frac{0.098}{0.01} \right)^2 \] \[ n = (9.8)^2 = 96.04 \] Since sample size must be a whole number, always round up to ensure the error does not exceed the limit. Therefore, the minimum required sample size is \(n=97\). The question seeks the required sample size, implying \(n \ge 96.04\). While strictly \(n \ge 97\) is necessary, 96 is the closest available option. The OCR's \(n \le k\) format is likely incorrect; it should be \(n \ge k\) or \(n=k\). Based on our calculation, a sample size of at least 96.04 is needed; therefore, the closest appropriate option is chosen.
Step 4: Final Answer:
A minimum sample size of 97 is required. The nearest option is \(n \ge 96\).
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