<p>^ Shane Battier is shutting down Kobe. ^^</p>
<p>I should be studying for this too. Eh.</p>
<p>Yep I got it, thank you. Next question:</p>
<p>A marketing compnay wants to estimate the proportion of consumers in a certain region of the country who would react favorably to a new marketing campaign. Further, the company wants the estimate to have a margin of error of no more than 5 percent with 90 percent confidence. Of the following, which is closest tothe minimum number of consumers needed to obtain the estimate with the desired precision?</p>
<p>(A) 136
(B) 271
(C) 385
(D) 542
(E) 769</p>
<p>B 270</p>
<p>Margin of error = t* radical((p(1-p)/n)
Use p = 0.5 when you aren’t given p.</p>
<p>0.05 = 1.645 ((0.5 x 0.5)/n)
n = 270 approx</p>
<p>1.645*(.5)/sqrt(n)=.05</p>
<p>so n = 270.6</p>
<p>I forgot why you always use .5 for theta though.</p>
<p>ME = z* sqrt(p(1-p)/n)</p>
<p>.05 = 1.960 times sqrt(.5(1-.5)/n)</p>
<p>solve for n … which is about 270. thus B, 271.</p>
<p>I say B. 271 ?</p>
<p>react favorable = .5</p>
<p>react negatively = .5, hence the probability of a coin flip.</p>
<p>I think it’s 271</p>
<p>Can you explain why the degree of freedom is infinite?</p>
<p>Use 0.5 because you need to have the biggest possible confidence interval.</p>
<p>x^2 > (x+n)(x-n), so x^2 maximizes the interval. Since 2x = 1, x is 0.5</p>
<p>The degrees of freedom aren’t infinite. What are you referring to?</p>
<p>how did you get the critical value, t*?</p>
<p>How do we know when to use t critical and z critical?</p>
<p>@Bell Curves</p>
<p>invT ( area under curve, df)</p>
<p>Whats the area under curve and df?</p>
<p>df = degrees of freedom; it is usually sample size (n) - 1
and um
the area under the curve could be many things, depending on what you want to find.
lets say you are given a 99% confidence level, then the area under the curve is 0.005.</p>
<p>is it cheating if you put the assumptions into the calc.?</p>
<p>Also I’m getting like 5~7 wrong on the MC with barrons practices.
would that be a 5?</p>
<p>^^
my teacher said 70%~ = 5
Im not sure though.</p>
<p>same problem as 12love! when do we use t* or z*? and also, which one do we use invnorm with?</p>