Question

Suppose that an anxiety measure has a mean of 114 and SD of 20. The researcher only wants to work with 33% of the lower participants. What is the smallest average score the researcher should consider with a sample size of 30?

Answer 1

Solution,

Given that,

mean = = 114

standard deviation = = 20

n = 30

= = 114

= / n = 20 / 30 = 3.65

Using standard normal table,

P(Z < z) = 33%

= P(Z < z) = 0.33  

= P(Z < -0.44) = 0.33

z = -0.44

Using z-score formula  

= z * +

= -0.44 * 3.65 + 114

= 112.39