yhc25 wrote:

On Jane's credit card account, the average daily balance for a 30-day billing cycle is the average (arithmetic mean) of the daily balances at the end of each of the 30 days. At the beginning of a certain 30-day billing cycle, Jane's credit card account had a balance of $600. Jane made a payment of $300 on the account during the billing cycle. If no other amounts were added to or subtracted from the account during the billing cycle, what was the average daily balance on Jane's account for the billing cycle?

(1) Jane's payment was credited on the 21st day of the billing cycle.

(2) The average daily balance through the 25th day of the billing cycle was $540.

It's bloodily wordy. can anyone please also explain the question?

"On Jane's credit card account, the average daily balance for a 30-day billing cycle is the average (arithmetic mean) of the daily balances at the end of each of the 30 days."

--> this part explaining definition of average daily balance.

Assume 1st is the begining of the cycle and 30the end of the billing cycle.

(1)

ADB = (600*20 + (600-300)*10 )/30

(2) let say payment credited on n+1 th day

ADB for 25 days = 540= (600*n+ 300(25-n))/25

--> 2n+25-n= 45 --> n=20

ADB for 30 days = (600*20 + (600-300)*10 )/30

D

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