prime number

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kanha81: Master | Next Rank: 500 Posts; Posts: 431; Joined: Sat Jan 10, 2009 9:32 amFollowed by: 1 member; Thanked: 16 times

by kanha81 » Mon Mar 02, 2009 11:47 am

q: If x is a prime number greater than 2, which of following is a prime number?
a) x^2
b) x/2
c) 3x
d) x-4
e) x^2+1

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Source: Beat The GMAT — Problem Solving | Mon Mar 02, 2009 11:47 am

marcusking: Master | Next Rank: 500 Posts; Posts: 106; Joined: Wed Feb 04, 2009 6:09 am; Location: Louisville, KY; Thanked: 8 times

Re: prime number

by marcusking » Mon Mar 02, 2009 12:01 pm

kanha81 wrote:q: If x is a prime number greater than 2, which of following is a prime number?
a) x^2
b) x/2
c) 3x
d) x-4
e) x^2+1

Not sure there is an answer to this that is always true.

a) If a prime number is squared it is divisible by itself so it's no longer prime
b) A prime number > 2 divided by 2 leaves a fraction which isn't a prime number.
c) any prime number multipled by 3 can also be divided by 3 making it not a prime number
d) 29 is prime 29-4 is 25 (not prime)
e)5^2 = 25. 25 + 1 = 26 (not prime)

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piyush_nitt: Master | Next Rank: 500 Posts; Posts: 424; Joined: Sun Dec 07, 2008 5:15 pm; Location: Sydney; Thanked: 12 times

Re: prime number

by piyush_nitt » Tue Mar 03, 2009 4:38 am

kanha81 wrote:q: If x is a prime number greater than 2, which of following is a prime number?
a) x^2
b) x/2
c) 3x
d) x-4
e) x^2+1

IMO D

x=7

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kamu: Senior | Next Rank: 100 Posts; Posts: 49; Joined: Fri Feb 27, 2009 12:41 amFollowed by: 3 members; Thanked: 44 times

Re: prime number

by kamu » Tue Mar 03, 2009 4:59 am

kanha81 wrote:q: If x is a prime number greater than 2, which of following is a prime number?
a) x^2
b) x/2
c) 3x
d) x-4
e) x^2+1

incorrect question i guess!

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abhijeetsinghai: Senior | Next Rank: 100 Posts; Posts: 39; Joined: Fri Jul 04, 2008 8:54 am; Location: US; Thanked: 1 times; GMAT Score:700

by abhijeetsinghai » Sat Mar 07, 2009 1:02 pm

Incorrect question....

D is wrong if x= 19, x-4=15, not prime

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karmayogi: Master | Next Rank: 500 Posts; Posts: 467; Joined: Thu Nov 06, 2008 10:19 pmFollowed by: 1 member; Thanked: 27 times

Re: prime number

by karmayogi » Sat Mar 07, 2009 1:20 pm

kanha81 wrote:q: If x is a prime number greater than 2, which of following is a prime number?
a) x^2
b) x/2
c) 3x
d) x-4
e) x^2+1

I guess, question has to be "which of following could be a prime numbre?" In that case, D will be the answer.

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--By Swami Vivekananda

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