Shortcut for Odd and Even number type questions : GMAT Quantitative Section
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Shortcut for Odd and Even number type questions

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Shortcut for Odd and Even number type questions [#permalink]

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21 Apr 2013, 11:02
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I have formulated a technique to solve type of 'Odd and Even number type questions' quickly, thus saving ample amount of time for other questions.
Basic concept used is of binary number calculations.

Binary Multiplication
0 * 0 = 0, 1 * 0 = 0, 1 * 0 = 0, 1 * 1 = 1

0 + 0 = 0, 1 + 0 = 1, 0 + 1 = 1
1 + 1 = 10 or 0 [For applying the technique we need to consider last digit of ‘10’ i.e. ‘0’]

Application of Technique
Odd Number => 1
Even Numbers => 0

a. Odd Number * Odd Number = Odd number
1 * 1 = 1

b. Odd Number * Even Number = Even Number
1 * 0 = 0

c. Even Number * Even Number = Even Number
0 * 0 = 0

d. Odd Number + Odd Number = Even Number
1 + 1 = 0

e. Even Number + Odd Number = Odd Number
0 + 1 = 1

f. Even Number + Even Number = Even Number
0 + 0 = 0

Usage in Exam
Ex:

Solve (odd + (even * even * (odd + even) + odd * (even +even)) +even *odd) ?
Solution: (1 + ( 0 * 0 * ( 1 + 0 ) + 1 * ( 0 + 0 )) + 0 * 1 )
= (1 + ( 0 * 1 +0 ) + 0)
= (1 + 0 + 0)
= 1 =>(Odd)

This equation can be solved mentally within 15secs.
This technique has helped me in solving these types of question within 30 seconds with practice and hence saving a lot of time.

Last edited by rohitkg on 17 May 2013, 22:54, edited 1 time in total.
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Re: Shortcut for Odd and Even number type questions [#permalink]

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21 Apr 2013, 23:32
Dude,

This is excellent stuff. Seriously it becomes so easy to remember with binary stuff. very nice ....

+1 Kudos to you definitely ...
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Re: Shortcut for Odd and Even number type questions [#permalink]

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23 Apr 2013, 10:07
igloo wrote:
Dude,

This is excellent stuff. Seriously it becomes so easy to remember with binary stuff. very nice ....

+1 Kudos to you definitely ...

Thanks ... good to know it was helpful
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Re: Shortcut for Odd and Even number type questions [#permalink]

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17 May 2013, 12:52
Nice application. Watch out for the typo in e & f.
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Re: Shortcut for Odd and Even number type questions [#permalink]

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17 May 2013, 21:38
As someone with a degree in Computer Science who owns several binary clocks (seriously I own more than one... it's a little weird!), I will say: Kudos. As pointed out above, you have slight typos in e) and f) regarding which term is even and which term is odd. I'd also be remiss if I didn't mention that this works just as well using the numbers 1 and 0 in non-binary applications. 0x1 is still 1, 0+0 is still 0. The only difference is 1+1 = 2, which is even. In actuality, you can just use odd or even number to prove the rule without ever having to reference binary.

Nonetheless, I find it useful and insightful to think about in terms of number properties. And if it works well for you and others, then good job taking something abstract and making it familiar with terms you already know well. Good job!

Ron
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Re: Shortcut for Odd and Even number type questions [#permalink]

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17 May 2013, 22:56
Nice application. Watch out for the typo in e & f.

Thanks for informing ... rectified the typo
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Re: Shortcut for Odd and Even number type questions [#permalink]

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05 Jun 2013, 02:04
This is awesome, thank you!!

As someone not familiar with binary, can you explain 1 + 1 = 10?

Also, anyone know other places to find tricks like these?
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Re: Shortcut for Odd and Even number type questions [#permalink]

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05 Jun 2013, 02:09
aceon wrote:
This is awesome, thank you!!

As someone not familiar with binary, can you explain 1 + 1 = 10?

Also, anyone know other places to find tricks like these?

Our Math Book is full of them: gmat-math-book-87417.html

Hope it helps.
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Re: Shortcut for Odd and Even number type questions [#permalink]

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15 Mar 2014, 14:24
thanks for this useful shortcut!!!

But, do you think it could be used for division somehow??
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Re: Shortcut for Odd and Even number type questions [#permalink]

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15 Mar 2014, 21:07
nicoki wrote:
thanks for this useful shortcut!!!

But, do you think it could be used for division somehow??

Hi Nicoki,

There is no rule as such for division of 'odd or even numbers' . Cause result can be fraction too in such cases.
Don't worry no one will ask you question based on Division. Atleast I have never come across any such question.

Best Regards,
Rohit Gupta
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Re: Shortcut for Odd and Even number type questions [#permalink]

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18 Aug 2015, 01:37
Hello from the GMAT Club BumpBot!

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Re: Shortcut for Odd and Even number type questions [#permalink]

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18 Aug 2016, 07:41
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: Shortcut for Odd and Even number type questions   [#permalink] 18 Aug 2016, 07:41
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