According to Moebs Services Inc., an individual checking account at major U.S. banks costs the banks between$350 and $450 per year. Suppose that the current average cost of all checking accounts at major U.S. banks is $400 per year with a standard deviation of $30. Let

x be the current average annual cost of a random sample of 225 individual checking accounts at major banks in America.

What is the probability that the average annual cost of the checking accounts in this sample is within $4 of the population mean?

What is the probability that the average annual cost of the checking accounts in this sample is less than the population mean by $2.70 or more?

Solution From the given information, for the annual costs of all individual checking accounts at major banks in America,

=$400and =$30

The mean and standard deviation of the sampling distribution of

x are, respectively,

x==$400 and x = $2.00

The probability that the mean of the annual costs of checking accounts in this sample is within $4 of the population mean is written as

P(396x404)Please explain how the 350 and 450 turned to this 396 and 404