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# Average Daily Balance from GMATprep

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Senior Manager
Joined: 06 Mar 2006
Posts: 475
Average Daily Balance from GMATprep [#permalink]

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21 Feb 2009, 19:53
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.

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Senior Manager
Joined: 08 Jan 2009
Posts: 310
Re: Average Daily Balance from GMATprep [#permalink]

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21 Feb 2009, 21:00
stmt 1 :

upto the 20th day the balance 600 and 21st day onwards balance 300.

so average balance of 30 day = (020 *600 + 300 * 10)/30. sufficient.

Stmt 2 :

The average balance till the 25 day = 540 \$
since there is no other transactions other than the 300\$.It is understood that the 300\$ payment has been made.So 26 day onwards balance = 300\$

average balance of 30 days = (25 * 540 + 5 * 300)/ 30 . Sufficient.

Ans is D.
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Re: Average Daily Balance from GMATprep [#permalink]

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21 Feb 2009, 21:04
eileen1017 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.

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 =600-300=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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Re: Average Daily Balance from GMATprep [#permalink]

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21 Feb 2009, 22:19
sondenso wrote:

-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

Nothing wrong with the wording..

No other amounts --> clearly "no othe amounts" --> other than above said amount (only payment of 300)
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Re: Average Daily Balance from GMATprep [#permalink]

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21 Feb 2009, 23:43
x2suresh wrote:
sondenso wrote:

-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

Nothing wrong with the wording..

No other amounts --> clearly "no othe amounts" --> other than above said amount (only payment of 300)

Thanks, I modified the post

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Re: Average Daily Balance from GMATprep   [#permalink] 21 Feb 2009, 23:43
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# Average Daily Balance from GMATprep

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