^{12}=.9978

1. According to a Pew Research Center poll, 40% of American college graduates have outstanding student loans. Suppose that this is true for the current population of American college graduates.

a. Find the probability that exactly 4 American college students in a sample of 12 have outstanding student loans.

b. Find the probability that at least one college student in a random sample of 12 have outstanding student loans.

c. What is the mean and standard deviation of a sample size of 12 from this population.

2. An average of .8 accidents occurs per day in a particular day in a particular large city.

a. Find the probability that 2 accidents occur in this city on a given day.

b. Find the probability that 10 accidents occur in this city in a given week.

c. What is the mean and standard deviation of this distribution in part a.

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1. Use the binomial distribution B(12,0.4) with a calculator.

a) P(X=4)=binomialpdf(12,0.4,4)=.2128

b) P(X≥1)=1-P(X=0)=1-0.6^{12}=.9978

c) µ=np=12*0.4=4.8, σ²=np(1-p)=12*0.4*0.6=2.88, σ=1.697

2. Use the Poisson distribution Pois(0.8) for a day or Pois(5.6) for a week with a calculator.

a) P(X=2)=poissonpdf(0.8,2)=.1438

b) P(X=10)=poissonpdf(5.6,10)=0.0309

c) µ=σ²=0.8, σ=0.8944

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## Comments

at leastone student has loans" is "no student has loans", so P(X=0)+P(X≥1)=1.