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When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7]

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When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7] [#permalink] New post 06 May 2012, 07:28
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Difficulty:

  35% (medium)

Question Stats:

49% (01:59) correct 51% (00:42) wrong based on 114 sessions
When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7]*[4]=?

A. [22]
B. [44]
C. [45]
D. [88]
E. [90]
[Reveal] Spoiler: OA
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Re: When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then [7] [#permalink] New post 06 May 2012, 09:13
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Galiya wrote:
When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then [7]*[4]=?

A. [22]
B. [44]
C. [45]
D. [88]
E. [90]

your thoughts?
i went with C and was happy till didn't see the official answer


[7]*[4]=(2*7+1)(4/2+1)=45.

Now, notice that the answer choices are also in boxes, so we have that [x]=45, which means that for even x it should be 45=x/2+1 --> x=88=even and for odd x it should be 45=x*2+1 --> x=22=even, so not a valid solution.

Answer: D. ([88]=88/2+1=45).

Similar question to practice: for-all-positive-integers-m-3m-when-m-is-odd-and-123618.html

Hope it helps.
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Re: When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then [7] [#permalink] New post 06 May 2012, 09:18
thanks, Bunuel! i was hoping for such an easy explanation
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Re: When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then [7] [#permalink] New post 26 Jun 2012, 02:42
Bunuel
was reviewing my posts and got a question (im pretty sure, after the explanation ill think- OMG it was so obvious, but anyway):
looking at the question above, why do we substitute [x], e.g. [7] or [4], instead of a and b?
x and a (or b) are not the same numbers.
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Re: When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then [7] [#permalink] New post 26 Jun 2012, 02:47
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Galiya wrote:
Bunuel
was reviewing my posts and got a question (im pretty sure, after the explanation ill think- OMG it was so obvious, but anyway):
looking at the question above, why do we substitute [x], e.g. [7] or [4], instead of a and b?
x and a (or b) are not the same numbers.


It should be: "When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7]*[4]=?"
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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. ,11 Mixed Questions, 12 Fresh Meat

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., 11 New DS set.


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Re: When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7] [#permalink] New post 26 Jun 2012, 03:00
+1 thank you for this and a lot of previous answers&explanations
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Re: When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7] [#permalink] New post 05 Oct 2013, 03:43
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Re: When X is even, [x]=x/2+1, when X is odd [x]=2x+1 then [7]   [#permalink] 05 Oct 2013, 03:43
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