You are wondering whether male or female students pay more for books and materials at the U of C. You find 5 male friends at the U of C and find that they spent an average of $680 with a standard deviation of $5. You find 4 female friends at the U of C and find that they spent an average of $690 with a standard deviation of $7. Is there a statistically significant difference in the average amount spent between the male and female friends (at α = .05)?

Answer 1

Z = (mean1 - mean2)/standard error (SE) of difference between means

SEdiff = √(SEmean1^2 + SEmean2^2)

SEm = SD/√n

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to your Z score.

Answer 2

Imagine that the probability of answering this question correctly is only p = .4, and on tests in which it is used, only 8 people attempt it. On what proportion of such tests will fewer than 3 people answer the question correctly?