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.

1.

What is the probability that the sample mean will be more than $306.60?

2.

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

z= 306.60-300/2.7712=2.3816

On table, 2.38= area of .4913, so .5-.4913=.0097

Can you help me understand my wrong answer?