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The positive integers r, s, and t are such that r is [#permalink]
 28 Jul 2010, 02:01
Question Stats:
25% (02:00) correct
75% (00:54) wrong based on 8 sessions
The positive integers r, s, and t are such that r is divisible by s and s is divisible by t. Is r even? (1) st is odd. (2) rt is even.
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Re: pretty hard one [#permalink]
28 Jul 2010, 02:22
mehdiov wrote: The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even. (1) st=odd, clearly not sufficient as no info about r, for example if r=6, s=1 and t=1 then answer is YES but if r=3, s=1 and t=1 then the answer is NO. (2) rt=even. For product of 2 integers to be even either one or both must be even. Can r not to be even? The only chance would be if t is even and r is odd. Let's check if this scenario is possible: if t is even, so must be s, as s is divisible by t (if an integer is divisible by even it's even too). Now, if s is even so must be r by the very same reasoning. So scenario when r is not even is not possible --> r=even. Sufficient. Answer: B.
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Re: pretty hard one [#permalink]
28 Jul 2010, 02:37
Bunuel wrote: mehdiov wrote: The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even. (1) st=odd, clearly not sufficient as no info about r, for example if r=6, s=1 and t=1 then answer is YES but if r=3, s=1 and t=1 then the answer is NO. (2) rt=even. For product of 2 integers to be even either one or both must be even. Can r not to be even? The only chance would be if t is even and r is odd. Let's check if this scenario is possible: if t is even, so must be s, as s is divisible by t (if an integer is divisible by even it's even too). Now, if s is even so must be r by the very same reasoning. So scenario when r is not even is not possible --> r=even. Sufficient. Answer: B. many thanks looks easy after the explanation  Do you have an idea about the level of this question ?
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Re: pretty hard one [#permalink]
28 Jul 2010, 02:44
mehdiov wrote: Bunuel wrote: mehdiov wrote: The positive integers r, s, and t are such that r is divisible by s
and s is divisible by t. Is r even?
(1) st is odd.
(2) rt is even. (1) st=odd, clearly not sufficient as no info about r, for example if r=6, s=1 and t=1 then answer is YES but if r=3, s=1 and t=1 then the answer is NO. (2) rt=even. For product of 2 integers to be even either one or both must be even. Can r not to be even? The only chance would be if t is even and r is odd. Let's check if this scenario is possible: if t is even, so must be s, as s is divisible by t (if an integer is divisible by even it's even too). Now, if s is even so must be r by the very same reasoning. So scenario when r is not even is not possible --> r=even. Sufficient. Answer: B. many thanks looks easy after the explanation Do you have an idea about the level of this question ? Not very hard (600+) but tricky, as it's C-trap question: the question which is obviously sufficient if we take statements together. When we see such questions we should become very suspicious.
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PLEASE READ AND FOLLOW: 11 Rules for Posting!!!
RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders
COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!! ,11 Mixed Questions NEW!!!, 12 Fresh Meat NEW!!!
DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!, 11 New DS set. NEW!!!
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Re: pretty hard one [#permalink]
07 Aug 2010, 03:44
Not very hard (600+) but tricky, as it's C-trap question: the question which is obviously sufficient if we take statements together. When we see such questions we should become very suspicious.[/quote] what is C-trap?
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Re: pretty hard one [#permalink]
07 Aug 2010, 05:47
Bunuel wrote:
(1) st=odd, clearly not sufficient as no info about r, for example if r=6, s=1 and t=1 then answer is YES but if r=3, s=1 and t=1 then the answer is NO.
Answer: B.
thanks...i was able to get to B but may be in 3 minutes..... i complicated the question thinking like 2 4 8 and not thinking infact one can be one number or 2 numbers can be same 8 2 2 and so on...
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Re: pretty hard one
[#permalink]
07 Aug 2010, 05:47
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