# Thread: Confidence Intervals #2

1. ## Confidence Intervals #2

I am having the hardest time grasping Confidence Intervals. I have several problems but I don't even understand the concept. Could be please break down how you got the answer.

The following data set represents the number of cars passing through an intersection between 4:30 and 5:30 p.m. for a random sample of 10 weekdays.

1207 1315 1005 1192 1108 1252 1179 1231 1098 1153

Calculate a 95% confidence interval for the population mean assuming the population of approximately normally distributed.

a. (116.5, 1231.5)

b. (1111, 1237)

c. (1001.4, 1346.6)

d. (974.8, 1373.2)

2. Calculate the Sample Mean
Calculate the Sample Standard Deviation
Look up or calculate the t-value for a 95% 2-tail test with nine degrees of freedom.

3. Confidence for the population mean is:

(x_bar) plus/minus (Z at 0.95/2) (s/sqrt(n))

What do you get for these parameters?

4. There are usually good videos covering this sort of thing over at the Khan Academy. Here is one for confidence intervals (I've not watched it so don't know how good it is however):

Confidence Interval Example | Khan Academy

Failing that, if you want a book that explains the basics of stats in a straightforward non-technical way then "Statistics for Dummies" by Deborah Rumsey-Johnson (PhD) has had some good reviews:

Statistics for Dummies: Amazon.co.uk: Deborah Rumsey-Johnson: Books

(Links to UK Amazon site but I'm pretty sure it's available in most countries).