Innocent until proven guilty? In Japanese criminal trials, about 95% of the defe
ID: 3356130 • Letter: I
Question
Innocent until proven guilty? In Japanese criminal trials, about 95% of the defendants are found guilty. In the United States, about 60% of the defendants are found guilty in criminal trials†. Suppose you are a news reporter following ten criminal trials. (a) If the trials were in Japan, what is the probability that all the defendants would be found guilty? (Round your answer to three decimal places.) What is this probability if the trials were in the United States? (Round your answer to three decimal places.) (b) Of the ten trials, what is the expected number of guilty verdicts in Japan? (Round your answer to two decimal places.) verdicts What is the expected number in the United Sates? (Round your answer to two decimal places.) verdicts What is the standard deviation in Japan? (Round your answer to two decimal places.) verdicts What is the standard deviation in the United States? (Round your answer to two decimal places.) verdicts (c) As a U.S. news reporter, how many trials n would you need to cover to be at least 99% sure of two or more convictions? trials How many trials n would you need if you covered trials in Japan?
Explanation / Answer
Ans:
a)Probability that all are found guilty(japan)=0.9510=0.599
Probability that all are found guilty(USA)=0.6010=0.006
b)
Expected number of gulity in Japan=np=10*0.95=9.5
Expected number of gulity in USA=10*0.6=6
standard deviation(Japan)=sqrt(10*0.95*0.05)=sqrt(0.475)=0.69
standard deviation(USA)=sqrt(10*0.6*0.4)=sqrt(2.4)=1.55
c)
Let n be the number of trials required.
P(x>=2)=1-P(x<=1)=1-BINOMDIST(1,n,0.6,TRUE)
For USA,
n should be 8 to be at least 99% sure of two or more convictions.
For Japan,
P(x>=2)=1-P(x<=1)=1-BINOMDIST(1,n,0.95,TRUE)
n should be 3 to be at least 99% sure of two or more convictions.
n 1-BINOMDIST(1,n,0.6,TRUE) 2 0.3600 3 0.6480 4 0.8208 5 0.9130 6 0.9590 7 0.9812 8 0.9915 9 0.9962 10 0.9983