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Joanna bought only $0.15 stamps and $0.29 stamps. How many

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Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 05 Jan 2010, 07:59
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A
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Difficulty:

  75% (hard)

Question Stats:

48% (01:07) correct 52% (01:18) wrong based on 33 sessions

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Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

(1) She bought $4.40 worth of stamps.
(2) She bought an equal number of $0.15 stamps and $0.29 stamps.

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/joanna-bought ... 01743.html

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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 05 Jan 2010, 08:25
A...
si) gives us total to be 4.4... for it to be true .29 cost stamps have to be in multiple of 5 as .15 ,the other cost is a multiple of 5....
possiblity of 5 or 10 or15 stamps of .29 cost.... a) 4.4-.29*5 is not divisible by .15 so not true..
b) 4.4-.29*10 is divisible by .15 so possible .. c) 4.4-.29*15 is not divisible by .15 so not true..
thus we get 10 of each...suff
sii) is not suff
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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 05 Jan 2010, 11:17
Good one. Answer is A
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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 28 Jul 2010, 06:49
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy ?
1 she bought $4.40 worth of stamps
2 She bought an equal number of $0.15 stamps and 0.29 stamps .

I was thinking we need the total stamps as an addtional information so I picked E !

pleas help me understand
thanks
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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 28 Jul 2010, 06:59
1
xmagedo wrote:
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy ?
1 she bought $4.40 worth of stamps
2 She bought an equal number of $0.15 stamps and 0.29 stamps .

I was thinking we need the total stamps as an addtional information so I picked E !

pleas help me understand
thanks


Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

Let \(x\) be the # of $0.15 stamps and \(y\) the # of $0.29 stamps. Note that \(x\) and \(y\) must be an integers. Q: \(x=?\)

(1) She bought $4.40 worth of stamps --> \(15x+29y=440\). Only one integer combination of \(x\) and \(y\) is possible to satisfy \(15x+29y=440\): \(x=10\) and \(y=10\). Sufficient.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps --> \(x=y\). Not sufficient.

Answer: A.

So when we have equation of a type \(ax+by=c\) and we know that \(x\) and \(y\) are non-negative integers, there can be multiple solutions possible for \(x\) and \(y\) (eg \(5x+6y=60\)) OR just one combination (eg \(15x+29y=440\)). Hence in some cases \(ax+by=c\) is NOT sufficient and in some cases it is sufficient.

For more on this type of questions check: gmat-prep2-92785.html?hilit=stamps

Hope it helps.
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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 29 Jul 2010, 02:44
Statement 1: equation 15x+29y=440
since both 15x and 440 are multiples of 5 then y=5, 10, 15, 20, ...
since 290y<440 then y<20 then y=5, 10, 15
since 15x mod 3 = 0, 29 mod 3 = 2, 440 mod 3 = 2, then y mod 3 = 1, or y=10
sufficient

Statement 2: clearly not sufficient

Notation: (a mod b) gives remainder when divide a by b
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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many  [#permalink]

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New post 14 Aug 2017, 01:55
Joanna bought only $0.15 stamps and $0.29 stamps. How many $0.15 stamps did she buy?

Let \(x\) be the # of $0.15 stamps and \(y\) the # of $0.29 stamps. Note that \(x\) and \(y\) must be an integers. Q: \(x=?\)

(1) She bought $4.40 worth of stamps --> \(15x+29y=440\). Only one integer combination of \(x\) and \(y\) is possible to satisfy \(15x+29y=440\): \(x=10\) and \(y=10\). Sufficient.

(2) She bought an equal number of $0.15 stamps and $0.29 stamps --> \(x=y\). Not sufficient.

Answer: A.

OPEN DISCUSSION OF THIS QUESTION IS HERE: http://gmatclub.com/forum/joanna-bought ... 01743.html

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.


If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many   [#permalink] 14 Aug 2017, 01:55
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