Search All of the Math Forum:
Views expressed in these public forums are not endorsed by
NCTM or The Math Forum.



Moore and McCabe Question
Posted:
Oct 28, 1996 3:06 AM


In the probability chapter, there is a question having to do with taking a poll about people who job. (p=.15) The poll is of 1500 people and the question states the average percent who job of the sample should be .15 with a standard deviation of .0092 It goes on to ask something else.
Thing is, though, since I know I'm about to ask questions regarding standard deviation of a repeated trial, I attempted to calculate the standard deviation myself. I don't get this value.
variance of one trial = (0.15)^2 (.85)+(1.15)^2 (.15)=.958375 SD of one trial = .978966
sd of 1500 trials = .02528
On a related question: I was attempting to calculate the probability of not losing money after betting craps 1000 times.
I found the odds of winning one bet was 49.292... As before I calculated the sd
mean = .01414...
var = (1+.01414)^2 (1.4929292)+ (1+.014141)^2 (.49292929) = .9998
sd = .9999
sd 1000 bets = .03162
Zscore of losing money= (0  (.01414))/.03162 = .4472 (I can't remember what percent this came out to but it was surprisingly low to me, I thought it would be a much more of a sure thing.) Am I missing something?



