compute probability that 12 people believe recession

gastonj

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Jul 24, 2007
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Fifty percent of Americans believed the country was in a recession, even though technically the economy had not shown two straight quarters of negative growth. For a sample of 20 Americans, make the following calculations.
a. Compute the probability that exactly 12 people believed the country was in a recession.

b. Compute the probability that no more than five people believed the country was in a recession.

Can someone help me with c and d?

c. How many people would you expect to say the country was in a recession?
would this be pp(1-p)?

d. Compute the variance and standard deviation of the number of people who believed the country was in a recession.
Would I use the number 12 from the people above?
 
factos9.gif

It works well with my $40 Computer Algebra System.
 
No, not if you set it up correctly.

a. \(\displaystyle \L\\C(20,12)(0.50)^{12}(0.50)^{8}\)

b. \(\displaystyle \L\\\sum_{k=1}^{5}C(20,k)(0.50)^{k}(0.50)^{20-k}\)
 
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