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Re: Joanna bought only $0.15 stamps and $0.29 stamps. How many
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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
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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 !

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

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

This is not a quality discussion. 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.