the mean amount of money spent per week on gas by a sample of 25 drivers was found to be $57.00 with a standard deviation of $2.
36. assuming the population distribution is normally distributed construct and interpret a 90% confidence interval for the mean amount of money spent on Gas per week
To construct a confidence interval we use the following formula:
ci = (sample mean) +- z*(sd)/[n^(1/2)]
The sample mean is 57, the standard deviation is 2.36, n s 25 and z is the upper (1-C)/2 critical value for the standard normal distribution. Here, as we want a confidence interval at a 90% we have (1-C)/2=0.05 we have to look at the 1-0.05=0.95 value at the normal distribution table, which is 1.65 approximately. Replacing all these values:
If they give you the total price and the price after the discount you can use this "formula" to solve it p/100=b/a where p is the percentage, a is the total price and b is the price after the discount.
