Imagine that Car Middle East, a car magazine is comparing that repair costs incurred during the first four years on two types of family car the Camry and Altima. Random samples of 60 Camry cars and 66 Altima cars are selected. The mean repair cost is $1,679 for Camry and $1,485 for Altima and with the sample standard deviation are $267 and $326 respectively. Assume that the distribution is normally distributed with equal variances.
a. find its pooled standard deviation.
b. based on the sample information, determine the 90% confidence interval estimate for the difference between two population mean.