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Question 685:



No answer provided yet.We need to estimate the sample size given a margin of error of 1.5 hours and level of confidence of 95%. The procedure to do this involves working backwards from the procedure used to generate a confidence interval. Recall that the confidence interval is 2 times the margin of error.  So we need to work backwards from the margin of error of 1.5 to find the sample size.
  1. First, we need to find the critical value for a 95% level of confidence, which we obtain from a table of normal values or the percentile to z-score calculator and we get 1.9599.
  2. Next, we divide the desired margin of error by the critical value = 1.5/1.9599 = .76532
  3. Divide the standard deviation by the result from step 2 = 6.4/.76532 = 8.362513
  4. Finally, we square the result from Step 3 = 69.93162.
Rounding up to the nearest student we should plan on 70 students.

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