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c and d are prime numbers. If c - d is an odd prime, then which of the

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c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even
[Reveal] Spoiler: OA

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Kudos [?]: 133161 [0], given: 12415

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 29 Oct 2017, 05:54
Bunuel wrote:
c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even



Hi...

c-d can be odd when one of the two is even and one odd..
c-d as odd prime means d is even prime and c is odd prime..
Odd-even=odd

D
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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 29 Oct 2017, 07:49
Bunuel wrote:
c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even


All prime numbers except 2 are odd, and we know ODD(Prime) - 2 = ODD(Prime)

So, correct answer will be (D) d is even

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 29 Oct 2017, 08:20
As c and d are primes, and c-d is also prime. So d is even.
Since 2 is the only even prime no. d = 2
So (D) is correct answer

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 30 Oct 2017, 21:40
Bunuel wrote:
c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even



If c-d is an odd prime then:
c>d
odd - odd = even
odd - even = odd
Since there is only 1 even prime number and it also happens to be the smallest prime, b MUST = 2 and thus D is the correct answer.

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 04 Nov 2017, 06:23
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We can solve this Sum by testing values.

c-d=Odd prime (given).
We can test this with the smallest prime nos. for simplicity: c=5,d=2 whose difference gives 3 another Odd prime.

Now as we found the values for c=5 and d=2,we can plug them in each ans.choice.

Only D is a Must Be True. Ans-D

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 04 Nov 2017, 10:13
Bunuel wrote:
c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even


Hi Bunuel,

Can you please help me to clarify my doubt for the above question. The question states that C & D are Prime Numbers and the option states that C & D are even/odd numbers. Is it right??

Also, odd prime numbers are all the prime numbers except 2 .. Am I right to think this??

Apologies if this is a stupid doubt :-)

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Re: c and d are prime numbers. If c - d is an odd prime, then which of the [#permalink]

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New post 05 Nov 2017, 01:13
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Expert's post
rahul16singh28 wrote:
Bunuel wrote:
c and d are prime numbers. If c - d is an odd prime, then which of the following must be true?

(A) c is even

(B) d is odd

(C) c*d is odd

(D) d is even

(E) c*d - c is even


Hi Bunuel,

Can you please help me to clarify my doubt for the above question. The question states that C & D are Prime Numbers and the option states that C & D are even/odd numbers. Is it right??

Also, odd prime numbers are all the prime numbers except 2 .. Am I right to think this??

Apologies if this is a stupid doubt :-)


The only even prime is 2. All other primes are odd.

2. Properties of Integers



For more check Ultimate GMAT Quantitative Megathread



Hope it helps.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 133161 [1], given: 12415

Re: c and d are prime numbers. If c - d is an odd prime, then which of the   [#permalink] 05 Nov 2017, 01:13
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