Question

An educational psychologist wishes to know the mean number of words a third grader can read per minute. She wants to ensure that the estimate has an error of at most 0.3 words per minute. A previous study found that the mean was 28.6 words per minute. Assuming that the standard deviation is 4.3, what is the minimum number of third graders that must be included in a sample to construct the 98% confidence interval? Round your answer up to the next integer.

Answer 1

Solution :

Given that,

standard deviation =s =   =4.3

Margin of error = E = 0.3

At 98% confidence level the z is ,

= 1 - 98% = 1 - 0.98 = 0.02

/ 2 = 0.02/ 2 = 0.01

Z/2 = Z0.01 = 2.33 ( Using z table    )

sample size = n = [Z/2* / E] 2

n = ( 2.33* 4.3 / 0.3 )2

n =1115.33

Sample size = n =1115