Explain what \"90% confidence\" means. Would a 95% confidence interval be wider

Question

Explain what "90% confidence" means. Would a 95% confidence interval be wider or narrow? Explain without actually calculating the interval. Language Neurological research has shown that in about 80% of people language abilities reside in the brain's left side. Another 10% display right-brain language centers, and the remaining 10% have two-sided language control (The latter two groups are mainly left-handers.) (Source: Science News, 161, no. 24 [2002]) We select 60 people at random. Is it reasonable to use a Normal model to describe the possible distribution of the proportion of the group that has left-brain language control? Explain. What's the probability that our group has at least 75% left-brainers? If the group had consisted of 100 people, would that probability be higher, lower, or about the same? Explain why, without actually calculating the probability How large a group would almost certainly guarantee at least 75% left-brainers? Explain. Cigarettes 2009 In 1999, the Centers for Disease Control and Prevention estimated that about 34.8% of high school students smoked cigarettes. They established a national health goal of reducing that figure to 16% by the year 2010. To that end, the would be on track if they achieved a reduction to 17.7% by 2009. In 2009, they

Explanation / Answer

a)
Yes, as the reason proportion rate is higher, the number of people fall in is higher rate
b)

Proportion ( P ) =0.8
Standard Deviation ( sd )= Sqrt (P*Q /n) = Sqrt(0.8*0.2/60)
Normal Distribution = Z= X- u / sd ~ N(0,1)"                  
"P(X < 0.75) = (0.75-0.8)/0.0516
= -0.05/0.0516= -0.969
= P ( Z <-0.969) From Standard Normal Table
= 0.1663"                  
P(X>=0.75) = 1 - P(X<0.75) = 1 - 0.1663 = 0.8337

c)
A group with 100 people will gives the similar probability. For any value of n, we compute the probability based on the value 100.

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