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Manager  B
Joined: 16 Jan 2011
Posts: 89
When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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6
11 00:00

Difficulty:   55% (hard)

Question Stats: 52% (01:20) correct 48% (01:15) wrong based on 463 sessions

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When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then * = ?

A. 
B. 
C. 
D. 
E. 
Math Expert V
Joined: 02 Sep 2009
Posts: 59598
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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5
5
Galiya wrote:
When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then *=?

A. 
B. 
C. 
D. 
E. 

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

*=(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.
_________________
##### General Discussion
Manager  B
Joined: 16 Jan 2011
Posts: 89
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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thanks, Bunuel! i was hoping for such an easy explanation
Manager  B
Joined: 16 Jan 2011
Posts: 89
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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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.  or , instead of a and b?
x and a (or b) are not the same numbers.
Math Expert V
Joined: 02 Sep 2009
Posts: 59598
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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1
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.  or , 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 *=?"
_________________
Manager  B
Joined: 16 Jan 2011
Posts: 89
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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+1 thank you for this and a lot of previous answers&explanations
Intern  Joined: 12 Dec 2013
Posts: 16
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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Bunuel wrote:
Galiya wrote:
When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then *=?

A. 
B. 
C. 
D. 
E. 

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

*=(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 V
Joined: 02 Sep 2009
Posts: 59598
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

### Show Tags

1
Rca wrote:
Bunuel wrote:
Galiya wrote:
When X is even, [x]=a/2+1, when X is odd [x]=2a+1 then *=?

A. 
B. 
C. 
D. 
E. 

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

*=(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 * = 45.

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

Does this make sense?
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Non-Human User Joined: 09 Sep 2013
Posts: 13729
Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *  [#permalink]

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_________________ Re: When x is even, [x] = x/2 + 1, when x is odd [x] = 2x + 1 then *   [#permalink] 15 Oct 2018, 07:18
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