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Statistics for Lawyers
Problem Set # 3–Due /04
Name_______________________________(Please print)
1. Compute the standard deviation (SD) for the numbers 1,2,3,4,5 (A) as if they are a
population. Now, assuming these numbers are a random sample, (B) compute the
standard error of the sample mean.
Ans.(A)_______________________________(B)_____________________________________
2. If an employer increases the salaries of his employees by $50, what dollar difference does
that make to (A) their average salary? (B) the SD of their salaries?
Ans. (A)_______________________________(B)_____________________________________
3. If an employer increases the salaries of his employees by 5%, what does that do to (A) their
average salary? (B) The SD of their salaries?
Ans.(A)_______________________________(B)_____________________________________
4. Three instructors are comparing notes on their finals; each had 99 students. In class A,
one student got a score of 1, another got a score of 99, and the rest got a score of 50. In
class B, 49 students got a score of 1, one student got a score of 50, and 49 students got a
score of 99. In class C, one student got a score of 1, one student got a score of 2, one
student got a score of 3, and so forth, all the way through 99. (A) Which class had the
highest average? Or are they the same? (B) Which class had the biggest SD? Or are they
the same? (C) Which class had the biggest range? Or are they the same?
Ans.(A)____________________(B)_____________________(C)___________________

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5. In a quality control program at a widget factory, widgets are weighed in batches to save
time. If the standard error involved in weighing good widgets is s gr per widget, (A) what
is the standard error of the total weight of a batch of n widgets (assuming that errors in
weight are not correlated)? (B) What is the standard error of the mean weight per widget
(again assuming independence of errors)? and (C) if the errors are positively correlated,
are the standard errors greater, less, or about the same as those given above?
Ans.(A)__________________(B)________________________(C)________________________
6. In the Florida 2000 presidential election, by one calculation, Bush’s projected plurality if
there had been a recount was eight standard errors from a tie. If Professor Chebyshev
were testifying, what would he say about the probability of such a large departure from a
tie, if the election really were a tie?
Ans.____________________________________________________________________
End of Problem Set # 3