Statdisk Notes for Activity 6

Finding the Critical Value (Question 6)

  1. Go to Analysis / Probability Distributions / Normal Distribution
  2. We need to enter the area to the left of the critical value in the "cumulative area from the left" box. Since the confidence level is 95%, there is 5% split between the two tails. That makes 2.5% in each tail. The area to the left of the left critical value is 2.5%, which is entered as the decimal 0.025.
  3. Click Evaluate

If you want the critical value on the right side, you can use the symmetry involved and just make the critical value you found above positive. Another way to find the critical value on the right directly is to repeat the steps above, but since there is 2.5% to the right of the right critical value, there is 97.5% to the left.

Finding the Margin of Error and Confidence Interval (Questions 7, 9)

  1. Go to Analysis / Confidence Intervals / Proportion One Sample
  2. The confidence level is 0.95 (95%)
  3. Enter the sample size and the number of successes (how many strawberries you had)
  4. Click Evaluate

The output will give the margin of error and the confidence interval.