PAM 2100 Exam #2 Review
Problem 1
A SRS of 1000 adults asks if they agree with the statement “I support President Obama.”
Suppose that 90% of all US adults would agree if asked this question so the population
parameter= 0.9.
Round the standard deviation of the sample proportion
p
ˆ
to four
decimal places
.
Using that rounded number, what is the probability that the survey result
differs from the truth about the population by more than 2 percentage points?
(Use z
scores that actually appear in Table A.
Round your final answer to four decimal places
.
Remember to express your answer as a proportion.)
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Melissa has invested 30% of her funds in Tbills and 70% of her funds in stocks.
If X is
the annual return on Tbills and Y the annual return on stocks, the portfolio rate of return
is:
R= 0.3X + 0.7Y
The returns X and Y are random variables because they vary from year to year:
X= annual return on Tbills
μ
X
= 5
σ
X
= 4
Y= annual return on stocks
μ
Y
= 12
σ
Y
= 6
correlation between X and Y
ρ = 0.4
a) What is μ
R
?
b) What is σ
R
? Round your final answer to four decimal places
.
2
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 Spring '08
 ABDUS,S.
 Standard Deviation, decimal places, erin

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