Question: Wachovia operates a network of automated teller machines (ATMs). On average a customer withdrawals $80 of cash each time. The bank estimates that the fixed cost of filling an ATM with cash is about $100 regardless of the amount of cash put in. Each month on average 600 customers use the ATM to withdrawal cash. How much cash should the bank keep at an ATM if its annual cost of money is 10%? How often should the bank replenish an ATM?