A bank has kept records of the checking balances of its customers and determined that the average daily balance of its customers is $300 with a standard deviation of $48. A random sample of 144 checking accounts is selected. Use attached normal dist. table.
What is the probability that the sample mean will be more than $306.60?
What is the probability that the sample mean will be less than $308?
I got the wrong answer of .0087
For 1, I used Sigma xbar=st. dev/sqrt. = 2.7712
On table, 2.38= area of .4913, so .5-.4913=.0097
Can you help me understand my wrong answer?