4. A bank has kept records of the checking balances of its customers and determined that the average daily balance of it

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4. 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.
a. What is the probability that the sample mean
will be less than $308?
b. What is the probability that the sample mean
will be between $302 and $308?
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