All freshmen at Success University take an orientation class. The professors plan on taking an SRS of 70 of the 800 freshmen and asking them twice whether they agree with the statement, "If I struggle with my homework, I
can find help once before the class and once after. They plan to look at the difference (after – before)
between the proportions of freshmen who agree with the statement. Suppose that before the class, 30% of the
freshmen agree, while after the class, 85% agree.
Consider the formula:
PA (1 - PA
Орд-ро ту
NA
PB (1 - PE
NB
Why is it not appropriate for the professors to use this formula for the standard deviation of the distribution of
the difference in sample proportions?