STAT
HW_7

# N100 x bar170000 sd10000 95 ci is 168040 171960 ans

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n=100 x-bar=170,000\$ sd=10,000\$ 95% CI is (168040, 171960) \$ ANS_________________ 15. Suppose a newspaper article reports that the average house price in Columbus OH is \$180,000. Do you agree with their report, based on your data from #37? EXPLAIN BRIEFLY. It is outside of 95% CI so it is very unlikely. 3

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YES NO #16-18: Suppose it is known that 30% of students at a particular college are smokers. 16. A sample of 5 students from that college is selected at random. Find the probability that the number of smokers in this sample is less than 4. P=0.3 n=5 k=0,1,2,3 P(x<4)=1-P(X=4)-P(X=5)=1-0.0308=0.9692 ANS _______________ 17. A sample of 100 students from the college is selected at random. Find the probability that the number of smokers in this sample is less than 40. np=30 n(1-p)=70 both are bigger than 10 so you can use normal approximation mean=30 std=4.58 P(X<40)=P(Z<2.18)=0.9854 18. There are 2 conditions that need to be met in order to be able to use the normal approximation. What is the minimum sample size needed in order to meet these two conditions in this particular situation (the smokers problem above)? 34 when n=34 np>10 n(1-p)>10 but n=33 doesn’t satisfy the first condition #19-20: Suppose the time to delivery of a package has a normal distribution with mean 2 days and standard deviation 0 .5 days. 19. What is the chance that one package selected at random took more than 2.2 days to deliver? P(X>2.2)=P(Z>(2.2-2)/0.5)=1-0.6554=0.3446 ANS___________ 20. What is the chance that 36 packages selected at random have an average delivery time of more than 2.2 days? P(X-bar>2.2)=P(Z>(2.2-2)/(0.5/6))=1-0.9918=0.0082 ANS____________ 4
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• Winter '07
• rumseyjohnson

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