# Thread: Urgent Having trouble

1. ## Urgent Having trouble

Hey I need to solve these 3 problems and I dont understand the formula's is just not clicking.

1.For this problem i need to construct the 90% and the 95% confidence intervals for the population mean and which one is wider.

From a random sample of 36 days in a recent year, the closing stock prices for hasbro had a mean of $19.31 and a standard deviation of$2.37

2.For this problem I need to construct the indicated confidence interval for the population mean u using (a) a t-distribution. (b) If you had a incorrectly used a normal distribution, which interval would be wider?

c= .95, x= 13.4, s= 0.85, n=8

3. Assume the variable is normally distruibuted and use a t-distribution to construct a 95% confidence interval for the population mean u, and what is the margin error of u?

In a random sample of five microwave ovens, the mean repair cost was $75.00 and the standard deviation was$12.50

I really need help with these problems i keep trying to get the formulas down but nothing sticking in my head when it come to confidence intervals. Thanks in advance to whom ever helps me.

2. Originally Posted by diabetesman
Hey I need to solve these 3 problems and I dont understand the formula's is just not clicking.

1.For this problem i need to construct the 90% and the 95% confidence intervals for the population mean and which one is wider.

From a random sample of 36 days in a recent year, the closing stock prices for hasbro had a mean of $19.31 and a standard deviation of$2.37

2.For this problem I need to construct the indicated confidence interval for the population mean u using (a) a t-distribution. (b) If you had a incorrectly used a normal distribution, which interval would be wider?

c= .95, x= 13.4, s= 0.85, n=8

3. Assume the variable is normally distruibuted and use a t-distribution to construct a 95% confidence interval for the population mean u, and what is the margin error of u?

In a random sample of five microwave ovens, the mean repair cost was $75.00 and the standard deviation was$12.50

I really need help with these problems i keep trying to get the formulas down but nothing sticking in my head when it come to confidence intervals. Thanks in advance to whom ever helps me.
If you search the MHF threads using key words such as

confidence interval

you will find several examples:

http://www.mathhelpforum.com/math-he...intervals.html

http://www.mathhelpforum.com/math-he...e-problem.html

http://www.mathhelpforum.com/math-he...on-normal.html

What difficulty are you having in applying the standard formulae?