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May 13th, 2017, 07:29 PM  #1 
Newbie Joined: May 2017 From: Texas Posts: 2 Thanks: 0  I need urgent Stats help on two questions.
I've barely got a grasp on my HS Stats class and its getting to that end of the year hurtle and i'm catching up on missed lessons while I was away. I will give many thanks to the kind one to lend a hand. 1) Check to see if the following sample sizes are large enough to be approximated by a normal curve? a) n = 50 & p = .3 e) n = 50 & p = .05 b) n = 15 & p = .45 f) n = 100 & p = .01 c) n = 100 & p = .7 g) n = 40 & p = .25 d) n = 60 & p = .25 h) n = 80 & p = .9 2) USA Today reported that 36% of adult drivers admit that they often or sometimes talk on a cell phone when driving. This was based on a random sample of 1004 adult drivers. a) What is a 90% confidence interval for the true proportion of adult drivers who have often or sometimes talk on a cell phone when driving? b) What is a 95% confidence interval for the true proportion of adult drivers who have often or sometimes talk on a cell phone when driving? c) What is a 99% confidence interval for the true proportion of adult drivers who have often or sometimes talk on a cell phone when driving? d) What do you notice? Last edited by kaid; May 13th, 2017 at 08:19 PM. 
May 14th, 2017, 03:37 PM  #2  
Senior Member Joined: Sep 2015 From: Southern California, USA Posts: 1,602 Thanks: 816  Quote:
Quote:
$\sigma = \dfrac{p(1p)}{\sqrt{1004}} \approx 0.00727$ a $90\%$ significance corresponds to a zscore of $z = \Phi^{1}\left(\dfrac{10.9}{2}\right) \approx 1.64485$ The $90\%$ confidence interval is thus $I_{0.9}=[0.36  z \sigma, ~0.36 + z\sigma] \approx [0.34804,0.37196]$ Quote:
what you observe should be intuitively clear.  

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