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# On jane's credit card account, the average daily balance for

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On jane's credit card account, the average daily balance for [#permalink]

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14 Jul 2008, 08:48
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I got this one wrong twice..can someone please give a detailed explanation...

On jane's credit card account, the average daily balance for a 30-day billing cycle is the average of the daily balances at the end of each of the 30 day. 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) Average daily balance through the 25th day of the billing cycle was \$450.

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Re: Gprep Avg/ Mean DS [#permalink]

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14 Jul 2008, 08:58
D it is IMHO.

1) monthly balance is (20*600 + 10*300)/30, suff

2) 540*25 = 13.500 you have to arrive to that in 25 steps, each one either 600 or 300. 600*20 + 300*5 = 13500, means the payments was made in the 21st day, suff

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Re: Gprep Avg/ Mean DS [#permalink]

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14 Jul 2008, 09:07
From statement 1)

av = (20*600 + 10*300)/30

From Statement 2)

Lets assume Jane deposited 300 dollars after x days:

[600*x + 300*(25-x) ] / 25 = 540

IMO D

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Current Student
Joined: 28 Dec 2004
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Kudos [?]: 319 [0], given: 2

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Schools: Wharton'11 HBS'12
Re: Gprep Avg/ Mean DS [#permalink]

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14 Jul 2008, 09:10
see my problem is what if \$300 that she deposited what if it gets credited in multiple chunks..i.e say \$100 on 21st day, \$50 on 22nd day..\$200 on 23 day..

i mean there is no mention that all the money gets credited immediatly??

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Re: Gprep Avg/ Mean DS [#permalink]

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14 Jul 2008, 09:19
it does say 1 payment in the question stem. but i see your point, in the real world, when you make a large deposite by check (\$5000+), the bank will credit you some fund immediately, but they will withhold the remainder amount until the check clear. I don't know if this applies to payments or not, but if you pay electronically with a sufficient balance, the whole amount clears the same day.

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Current Student
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Re: Gprep Avg/ Mean DS [#permalink]

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14 Jul 2008, 09:25
well..i think this question is making you assume that it will be cleared in 1 payment...somehow i cannot make that leap of faith unless its catagorically mentioned..

i am reading too much into this??

gmatnub wrote:
it does say 1 payment in the question stem. but i see your point, in the real world, when you make a large deposite by check (\$5000+), the bank will credit you some fund immediately, but they will withhold the remainder amount until the check clear. I don't know if this applies to payments or not, but if you pay electronically with a sufficient balance, the whole amount clears the same day.

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Re: Gprep Avg/ Mean DS [#permalink]

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17 Jul 2008, 18:07
I'm getting D.

State 1: We know it was credited on the 21st day...thats when it hit the balance. everyday after that is 300. we can find the 30 day avg.

State 2: we know the sum of day 1 --> 25th...since the avg is \$540 we know the payment was made in there someplace...so the remaining days are \$300 balance. We can find avg of the 30 days.

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Re: Gprep Avg/ Mean DS [#permalink]

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06 Dec 2009, 21:51
I know this is an old post, but to be honest, I am having difficulty just understand the concept of this question.

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Re: Gprep Avg/ Mean DS [#permalink]

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06 Dec 2009, 21:54
Originally it says her balance is \$600, but it doesn't say whether it is her monthly or daily balance. In my head, I was thinking, that's a large daily balance to have on her credit card bill, so I thought she would initially have to pay off \$600, and somewhere in the month she made a payment of 300, which was on the 21st day.

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Re: Gprep Avg/ Mean DS   [#permalink] 06 Dec 2009, 21:54
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