A bank pays interest to its customers on the last day of the year. The interest paid to a customer
is calculated as 10% of the average monthly balance maintained by the customer. John is a
customer at the bank. On the last day, when the interest was accumulated into his account, his
bank balance doubled to $5760. What is the average monthly balance maintained by John in his
account during the year?  Answers:
A) 2840 B) 28800 C) 6840 D) 7540 E) 28400
bank balance is doubled with accumulation of interest tp 5760..   this means INTEREST is   5760/2= 
<gadget id="calculator">  5760/2</gadget>
<output>2_880</output>
2880 for entire year..   although since interest is 10% of avg MONthly balance, it becomes 28800..   28800
<result>B</result>
A bank pays interest to its customers on the last day of the year. The interest paid to a customer
is calculated as 10% of the average monthly balance maintained by the customer. John is a
customer at the bank. On the last day, when the interest was accumulated into his account, his
bank balance doubled to $5760. What is the average monthly balance maintained by John in his
account during the year?