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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] New post 21 Dec 2010, 08:26
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On Jane's credit card account, the average daily balance for 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 substracted 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.
[Reveal] Spoiler: OA

Last edited by Bunuel on 21 Dec 2010, 08:31, edited 1 time in total.
Edited the stem.
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Re: on the janes credit card [#permalink] New post 21 Dec 2010, 09:24
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anilnandyala wrote:
On Jane's credit card account, the average daily balance for 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 substracted 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.


Question basically ask on which day did Jane make the payment of $300.

Or algebraically: average \ daily \ balance=\frac{x*600+(30-x)*300}{30} --> for the first x days the balance will be $600 and then for (30-x) days the balance will be $600-$300=$300 (meaning that Jane made a payment of $300 on the (x+1)st day). So all we need to know is on which day did Jane make the payment of $300, the value of x+1.

(1) Jane's payment was credited on the 21st day of the billing cycle --> directly gives the value of x+1 --> x+1=21 --> x=20: for 20 days the balance was $600 and for the rest 10 days (from 21st) it was $300 --> we can find the average daily balance. Sufficient.

(2) The average daily balance through the 25th day of the billing cycle was $540 --> average_{25 \ days}=540=\frac{x*600+(25-x)*300}{25} --> we can find x --> we can find the average daily balance. Sufficient.

Answer: D.
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Re: Credit card payments....DS word problem [#permalink] New post 31 Dec 2010, 04:37
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1)you know that for the first 20 days you have a balance of 600, for the following a balance of 300 and then just averaging

2)you know that for the first 25 days the average balance is 540 and for the following days you have a balance of 300 each. Just take 25*540 + 5*300 and divide it by 30 again ...

Hope I could help you!
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 19 Nov 2011, 22:39
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At the staring of the month we have 600$. Some where in the middle 300$ is withdrawn. If we know the date when this happened or the average on a date after the amount is withdrawn. We can find a soln.

S1: amount withdrawn on 21st. Hence :

av = (20*600+10*300)/30
av = 500. Sufficient

S2: given av as 540 on 25th. As the average is less than 600$ we know as of 26th the amount in the account is 300$.

hence
av= (25*540+5*300)/30
av= 500
Sufficient.

Hence D
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 05 Jul 2012, 21:02
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smartmanav wrote:
I need more help here :(
read the 2nd statement : The average daily balance through the 25th day of the billing cycle was $540.

Perhaps the payment was deducted from her account n 27th day but they just provided the avg for first 25 days , in that case we will not be able to solve it. No ??


The average of the 25 days is $540. If the average were $600, only then can we say that the deduction was made after the 25th day. Since the average is less than $600, the deduction must have been made before the 25th day. Only then can the average be less than 600.

Now, it is simple to find the average (even though you don't need to)

For 25 days, the average balance was $540 and for 5 days, it was $300.

Avg = (540*25 + 300*5)/30 = 500
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Re: Credit card payments....DS word problem [#permalink] New post 31 Dec 2010, 08:45
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Could someone please help me with this one?

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 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.

Thanks!

Long question stem... Though try to identify that the question is just testing you on weighted averages. For some days the account had $600, for rest of the days, the account had $300 in it. We need to find the average of the amount in the account (it is weighted because the two amounts could have been in the account for different durations.)

Stmnt 1 - We know now that the account had $600 for 20 days and $300 for the rest of the 10 days. You can easily find the average. Sufficient.

You don't need to since it is a DS question, but if you had to find the average, then Avg = (600*20 + 300*10)/30 = 500
or using scale method:
Attachment:
Ques1.jpg
Ques1.jpg [ 3.77 KiB | Viewed 6284 times ]


Stmnt 2 - Average for first 25 days = 540 so you can find for how many of these 25 days, the account balance was 600 and for how many was it 300. The rest of the 5 days, the balance was of course $300. Hence sufficient.

If you want to do the calculations:
Attachment:
Ques2.jpg
Ques2.jpg [ 3.9 KiB | Viewed 6281 times ]


No of days $300 balance : No of days $600 balance = 1:4
So out of 25 days, (1/5)*25 = 5 days, the balance was $300.
(4/5)*25 = 20 days the balance was $600.

Answer (D)
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Re: Credit card payments....DS word problem [#permalink] New post 22 Feb 2011, 12:11
VeritasPrepKarishma wrote:
jonblazon wrote:
Could someone please help me with this one?

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 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.

Thanks!

Long question stem... Though try to identify that the question is just testing you on weighted averages. For some days the account had $600, for rest of the days, the account had $300 in it. We need to find the average of the amount in the account (it is weighted because the two amounts could have been in the account for different durations.)

Stmnt 1 - We know now that the account had $600 for 20 days and $300 for the rest of the 10 days. You can easily find the average. Sufficient.

You don't need to since it is a DS question, but if you had to find the average, then Avg = (600*20 + 300*10)/30 = 500
or using scale method:
Attachment:
Ques1.jpg


Stmnt 2 - Average for first 25 days = 540 so you can find for how many of these 25 days, the account balance was 600 and for how many was it 300. The rest of the 5 days, the balance was of course $300. Hence sufficient.

If you want to do the calculations:
Attachment:
Ques2.jpg


No of days $300 balance : No of days $600 balance = 1:4
So out of 25 days, (1/5)*25 = 5 days, the balance was $300.
(4/5)*25 = 20 days the balance was $600.

Answer (D)


Interesting approach but i find the algebraic formula easier. Esp for the second statement. This seems time consuming
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On Jane's credit card account, the average daily balance for [#permalink] New post 18 Nov 2011, 13:05
On Jane's credit card account, the average daily balance for a 30-day billing cycle is average (arithmetic mean) of the daily balances at the end 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 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.

Struggling to solve this. Can you please help? OA is not provided. :cry:
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 04 Feb 2012, 13:17
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enigma123 wrote:
On Jane's credit card account, the average daily balance for a 30-day billing cycle is average (arithmetic mean) of the daily balances at the end 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 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.

Struggling to solve this. Can you please help? OA is not provided. :cry:


Merging similar topics. Please ask if anything remains unclear.
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 05 Jul 2012, 18:06
I need more help here :(
read the 2nd statement : The average daily balance through the 25th day of the billing cycle was $540.

Perhaps the payment was deducted from her account n 27th day but they just provided the avg for first 25 days , in that case we will not be able to solve it. No ??
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 10 Oct 2012, 05:23
VeritasPrepKarishma wrote:
smartmanav wrote:
I need more help here :(
read the 2nd statement : The average daily balance through the 25th day of the billing cycle was $540.

Perhaps the payment was deducted from her account n 27th day but they just provided the avg for first 25 days , in that case we will not be able to solve it. No ??


The average of the 25 days is $540. If the average were $600, only then can we say that the deduction was made after the 25th day. Since the average is less than $600, the deduction must have been made before the 25th day. Only then can the average be less than 600.

Now, it is simple to find the average (even though you don't need to)

For 25 days, the average balance was $540 and for 5 days, it was $300.

Avg = (540*25 + 300*5)/30 = 500


this is good stuff! Nice!

thanks....
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Re: On Jane's credit card account, the average daily balance for [#permalink] New post 28 Nov 2013, 04:50
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Re: on the janes credit card [#permalink] New post 28 Nov 2013, 04:55
Bunuel wrote:
anilnandyala wrote:
On Jane's credit card account, the average daily balance for 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 substracted 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.


Question basically ask on which day did Jane make the payment of $300.

Or algebraically: average \ daily \ balance=\frac{x*600+(30-x)*300}{30} --> for the first x days the balance will be $600 and then for (30-x) days the balance will be $600-$300=$300 (meaning that Jane made a payment of $300 on the (x+1)st day). So all we need to know is on which day did Jane make the payment of $300, the value of x+1.

(1) Jane's payment was credited on the 21st day of the billing cycle --> directly gives the value of x+1 --> x+1=21 --> x=20: for 20 days the balance was $600 and for the rest 10 days (from 21st) it was $300 --> we can find the average daily balance. Sufficient.

(2) The average daily balance through the 25th day of the billing cycle was $540 --> average_{25 \ days}=540=\frac{x*600+(25-x)*300}{25} --> we can find x --> we can find the average daily balance. Sufficient.

Answer: D.



Bunuel, what is the purpose of the first sentence in the question. Has it been mentioned to simply confuse or am I missing something?
Re: on the janes credit card   [#permalink] 28 Nov 2013, 04:55
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