When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] : GMAT Problem Solving (PS)
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# When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4]

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Manager
Joined: 15 Jan 2011
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Kudos [?]: 155 [1] , given: 13

When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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06 May 2012, 07:28
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Question Stats:

49% (01:58) correct 51% (00:44) wrong based on 289 sessions

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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
Math Expert
Joined: 02 Sep 2009
Posts: 36520
Followers: 7067

Kudos [?]: 92936 [5] , given: 10528

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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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]

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.

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

Hope it helps.
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Manager
Joined: 15 Jan 2011
Posts: 103
Followers: 11

Kudos [?]: 155 [0], given: 13

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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06 May 2012, 09:18
thanks, Bunuel! i was hoping for such an easy explanation
Manager
Joined: 15 Jan 2011
Posts: 103
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Kudos [?]: 155 [0], given: 13

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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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.
Math Expert
Joined: 02 Sep 2009
Posts: 36520
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Kudos [?]: 92936 [1] , given: 10528

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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26 Jun 2012, 02:47
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Expert's post
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]=?"
_________________
Manager
Joined: 15 Jan 2011
Posts: 103
Followers: 11

Kudos [?]: 155 [0], given: 13

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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26 Jun 2012, 03:00
+1 thank you for this and a lot of previous answers&explanations
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Kudos [?]: 163 [0], given: 0

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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05 Oct 2013, 03:43
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

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Kudos [?]: 7 [0], given: 34

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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03 Nov 2014, 07:47
Bunuel wrote:
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]

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.

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

Hope it helps.

Hi Bunuel,

Why do we not consider 22 as an answer? Is it because 22 as an answer was even when equated to an odd equation, i.e 2a+1? Does the solution also
have to be odd when equated to an odd equation (2a+1)?
I hope my question makes sense ... not sure if I was able to explain myself clearly? =P Please let me know!

Thanks as always!!
Math Expert
Joined: 02 Sep 2009
Posts: 36520
Followers: 7067

Kudos [?]: 92936 [1] , given: 10528

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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03 Nov 2014, 07:58
1
KUDOS
Expert's post
Rca wrote:
Bunuel wrote:
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]

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.

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

Hope it helps.

Hi Bunuel,

Why do we not consider 22 as an answer? Is it because 22 as an answer was even when equated to an odd equation, i.e 2a+1? Does the solution also
have to be odd when equated to an odd equation (2a+1)?
I hope my question makes sense ... not sure if I was able to explain myself clearly? =P Please let me know!

Thanks as always!!

We got that [7]*[4] = 45.

Now, [22], since 22 is even, is 22/2 + 1 = 12, not 45.

Does this make sense?
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Joined: 09 Sep 2013
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Kudos [?]: 163 [0], given: 0

Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4] [#permalink]

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15 Apr 2016, 10:24
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then [7]*[4]   [#permalink] 15 Apr 2016, 10:24
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