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.