GMAT Changed on April 16th - Read about the latest changes here

It is currently 23 Apr 2018, 00:51

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Sneaky or indirect ways the GMAT uses to tell you a variable is odd

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Manager
Manager
avatar
B
Joined: 26 Feb 2018
Posts: 67
Location: United Arab Emirates
GMAT 1: 710 Q47 V41
GMAT 2: 770 Q49 V47
Reviews Badge CAT Tests
Sneaky or indirect ways the GMAT uses to tell you a variable is odd [#permalink]

Show Tags

New post 24 Mar 2018, 16:01
1
This post was
BOOKMARKED
I'll go first with the ones I've seen, add yours below.

Remember, if n is odd then n is also NOT EVEN and therefore not equal to zero, 2, 4 or any even number, and does not have units digit of 0, 2, 4, 6 or 8, etc. If we know n is odd, then we can definitively answer such question as "is n even?" or "is n a multiple of 4?" or "is n a factor of 2^x (x>0)?" with NO and therefore such statements may be sufficient for DS purposes.

Knowing if n is odd also helps us answer data sufficiency questions when we have previously calculated two different values for n, one odd one even, and the question is asking us for one discreet value of n.

Some statements are sufficient on their own, some need additional information

These are all assuming that we already know that n is an integer

- n is a prime greater than 2
- n is a prime number and n is not equal to 2
- n is not a multiple of 2
- n does not have 2 as a factor
- n/2 is not an integer (must know than n is an integer!)
- n is the square of a prime number and is greater than 4
- n is the product of 2 primes that are both greater or not equal to 2 (or n is 2/4/6/any even number more/less than this product (which must be odd) May be written as something like "n+4 the product of...")
- n is one less/one more than the sum of two prime numbers greater than 2 (may also be expressed as "n+1 is...." or "n-1 is....". Anyway, the sum of two primes that are both greater than 2 is always even. If n is 1/3/5/any odd number more or less than this sum (which must be even) then n is odd)
- (-1)^n is less than zero
- (-m)^n is less than zero (we don't need to know about m. M must be positive for any value of (-m)^n to be less than zero. If m is negative, -m is positive and (-m)^n can never be less than 0)
- n is a prime number between x and y (when x is more than 2, y could be anything)
- n is a product of two prime numbers between x and y (they could give any values here but x must be more than 2)
- n^2 is an odd number
- n^3 is an odd number
- n^x is an odd number and x is not equal to zero (Careful!! n^x will always be odd if n is odd. However, if x is 0, n^x will be equal to 1, and is therefore odd when n is both even or odd. This is a sneaky way a DS question can trick you into thinking n is odd, when it might not be. Unless you know that x is not equal to zero, "n^x is odd" does not necessarily mean n is odd and alone is insufficient to determine whether n is odd.)
- the units digit of n is a prime number greater than 2
- 2^n has a units digit of 2 (this means that n is 1, 5, 9 etc - always odd)
- 2^n has a units digit of 8 (this means that n is 3, 7, 11 etc - always odd)
- 9^n has a units digit of 9 (same theme. There are several variations on this)
- m*n is odd (we must know that m and n are integers)
- m^n = m, and m is not equal to 0 or 1 (If m is -1, n can be any odd number. For other values of m, n must be equal to 1, which is odd. The question may express the conditions as some thing like m>1)
- n/3 is an odd integer (this tells you that n is an odd multiple of 3) (there can be many variations on this. To generalise, if the statement gives you any variation of "n^x/y = an odd integer" and y is an odd integer and x is not zero, we know n must be odd)
- m+n is an even number and m is odd (might be told that m is odd in any of the ways above, or given a direct value of m e.g. m=5, or given information that allows the calculation of m)

And some phrases used that on their own do NOT definitively tell you whether n is odd or even
- 1/n is a terminating decimal (1/5 and 1/2 are both terminating)
- 1/n is a repeating decimal (1/3 and 1/6 are both repeating)
- the reciprocal of the units digit of n is a repeating decimal/terminating decimal (see above. The question may then go on to tell you something else, such as "5 is not a factor of n", that allows you to determine the u.d. of n)
- n^x is an odd number (see above. X could be equal to zero, in which case n^x =1 for all values of n, odd and even)
- (-m)^n is positive (unlike the example above, in this case we do need to know if m is positive or negative, and cannot assume)
- n is prime
- 6^n has a units digit of 6/5^n has a units digit of 5
- 1^n is odd (1^n = 1 for all values of n, so it's always odd)
- m^n = m (this phrase tricks you into thinking that maybe n=1, but in fact we could have m=1 and any value of n, including zero)
- n is the product of two prime numbers
- n is the sum of two prime numbers
Expert Post
Manhattan Prep Instructor
User avatar
S
Joined: 04 Dec 2015
Posts: 509
GMAT 1: 790 Q51 V49
GRE 1: 340 Q170 V170
Re: Sneaky or indirect ways the GMAT uses to tell you a variable is odd [#permalink]

Show Tags

New post 25 Mar 2018, 13:35
Here's a fun one:

n = 2k+1, where k is an integer. (Alternatively, n = 2k-1.)
_________________

Image

Chelsey Cooley | Manhattan Prep Instructor | Seattle and Online

My upcoming GMAT trial classes | GMAT blog archive

Expert Post
Top Contributor
SVP
SVP
User avatar
P
Joined: 12 Sep 2015
Posts: 2298
Location: Canada
Re: Sneaky or indirect ways the GMAT uses to tell you a variable is odd [#permalink]

Show Tags

New post 25 Mar 2018, 14:45
Expert's post
Top Contributor
When positive integer n is divided by 2, the remainder is 1
_________________

Brent Hanneson – Founder of gmatprepnow.com

Image

Re: Sneaky or indirect ways the GMAT uses to tell you a variable is odd   [#permalink] 25 Mar 2018, 14:45
Display posts from previous: Sort by

Sneaky or indirect ways the GMAT uses to tell you a variable is odd

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.