A sample of 81 account balances of a credit company showed an average balance of $1,200 with a standard deviation of $126. You want to determine if the mean of all account balances is significantly...

A sample of 81 account balances of a credit company showed an average balance of $1,200 with a standard deviation of $126.  You want to determine if the mean of all account balances is significantly different from last years average balance of $1,150.  Use a .05 level of significance.

State the null and alternative hypothesis.

What is the rejection rule?

Compute the value of the test statistic z.

What is the conclusion?