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Manager  Joined: 22 Jul 2008
Posts: 78
Location: Bangalore,Karnataka
Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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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.

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Math Expert V
Joined: 02 Aug 2009
Posts: 7688
Re: Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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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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Manager  Joined: 27 Aug 2009
Posts: 78
Re: Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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Good one. Answer is A
Manager  Joined: 09 Jun 2010
Posts: 59
Re: Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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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 . I was thinking we need the total stamps as an addtional information so I picked E ! pleas help me understand thanks Math Expert V Joined: 02 Sep 2009 Posts: 55277 Re: Joanna bought only$0.15 stamps and $0.29 stamps. How many [#permalink] ### Show Tags 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.
_________________
Intern  Joined: 03 Mar 2010
Posts: 37
Re: Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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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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Math Expert V
Joined: 02 Sep 2009
Posts: 55277
Re: Joanna bought only $0.15 stamps and$0.29 stamps. How many  [#permalink]

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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.

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

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