A researcher is interested in determining the average number of years new teachers remain in the classroom. If past information shows a standard deviation of 5 years, what size sample should be taken so that at 95% confidence the margin of error will be 6 months or less?

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Given: error: 6 months, standard deviation = 5 years is 60 months

Step 1: find the minimal sample size ‘n’ for 95% confidence interval

1-0.95= 0.05

0.05/2= 0.025

Step 2:
1-0.025= 0.975

View attachment for more steps

Okay. 12 - 4 is 8. For the other question, you have to multiply the difference of that by 1/4. 8 * 1/4 is 2. The expression of (12 - 4) is four times the value of 1/4 * (12 - 8). and 2 is 1/4 the value of 8. The answers to this question are A , B, and C.