eileen1017 wrote:
On Jane's credit card account, the average daily balance for a 30day 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 30day 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.
Please give your detailed explanation. Thanks.
The wording made a little confusing.
But you should focus largely on the following reasons:Jane made
ONLY a payment of $300 on the account during the billing cycle

no other amounts were added to or subtracted from the account during the billing cycle
1.
day1: balance=600
day2: balance =600
......
day 20: balance=600
day 21: balance =600300=300
day 22: balance = 300
.....
day 30: balance =300
Total=600*20 + 300*10,> average can be determined, Suff
2.
Since the average of 25 days =540, smaller than 600, the payment must be done at sometime before the date of 25th. So the remaining 5 days, each must have the balance of 300. The total of balance of the remaining 5 days =5*300 and the total balance of 25days =540*25
Total balance of 30 days can be determined, and so the average. Suff
D is the best
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