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Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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25 Nov 2010, 16:36
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Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a prime number My solution: (1) A+1 is a prime number if A=1, A+1 =2 which is prime, but A is not divisble by 3, whereas if A=6, A+1 =7 which is prime, A is divisible by 3 Hence (1) is Not Sifficient
(2) A1 is prime is A= 6, A1 = 5 which is prime, A is divisible by 3 but if A=8, A1=7 which is prime, A is not divisible by 3
(1)+(2) the numbers A1,A,A+1 are consequtive numbers such that A1 & A+1 are prime numbers.
Such pairs are 3,4,5A=4, not divisible by 3 11,12,13A=12, divisible by 3 17,18,19A=18, divisible by 3
Hence Answer is E
Is this solution correct?
Thanks NAD
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Re: Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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26 Nov 2010, 05:25
nades09 wrote: Is A divisible by 3?
(1) A+1 is a prime number (2) A1 is a prime number
My solution: (1) A+1 is a prime number if A=1, A+1 =2 which is prime, but A is not divisble by 3, whereas if A=6, A+1 =7 which is prime, A is divisible by 3 Hence (1) is Not Sifficient
(2) A1 is prime is A= 6, A1 = 5 which is prime, A is divisible by 3 but if A=8, A1=7 which is prime, A is not divisible by 3
(1)+(2) the numbers A1,A,A+1 are consequtive numbers such that A1 & A+1 are prime numbers.
Such pairs are 3,4,5A=4, not divisible by 3 11,12,13A=12, divisible by 3 17,18,19A=18, divisible by 3
Hence Answer is E
Is this solution correct?
Thanks NAD Prime numbers proerty: Exept 2, all the other prime #s are ODD... qtn: is A=3K, for any integer K. stmnt 1: A+1 is a prime number case1a: A+1 not = 2 but some other prime # then A+1, prime , is an ODD # ==> A is an EVEN that may be divisible by 3. e.g 12 case1b: A+1= 2, prime # then A = 1 , not divisible by 3 but due to case 1a we can not answer the qtn: hence stmnt 1 NOT SUFF stmnt 2: A1 is a prime number case2a: A1 not = 2 but some other prime # then A1, prime , is an ODD # ==> A is an EVEN that may be divisible by 3. e.g 12 case2b: A1= 2, prime # then A = 3 , and divisible by 3 but due to case 2a we can not answer the qtn: hence stmnt 2 NOT SUFF 1&2 together will eliminate case1b and case2b (as both A1 and A+1 can not be = 2) and retain case1a and case2a that say that A is an EVEN but nothing else abt A hence 1&2 together NOT SUFF. answer "E" Regards, Murali. kudos?



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Re: Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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28 Nov 2010, 08:41
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nades09 wrote: Is A divisible by 3?
(1) A+1 is a prime number (2) A1 is a prime number
My solution: (1) A+1 is a prime number if A=1, A+1 =2 which is prime, but A is not divisble by 3, whereas if A=6, A+1 =7 which is prime, A is divisible by 3 Hence (1) is Not Sifficient
(2) A1 is prime is A= 6, A1 = 5 which is prime, A is divisible by 3 but if A=8, A1=7 which is prime, A is not divisible by 3
(1)+(2) the numbers A1,A,A+1 are consequtive numbers such that A1 & A+1 are prime numbers.
Such pairs are 3,4,5A=4, not divisible by 3 11,12,13A=12, divisible by 3 17,18,19A=18, divisible by 3
Hence Answer is E
Is this solution correct?
Thanks NAD Possible values of A using S1: 1,2,4,6,10,12..... NOT SUFFICIENTPossible values of A using S2: 3,4,6,8,12......... NOT SUFFICIENTCommon values in both the lists: 4,6,12........... NOT SUFFICIENTAnswer: E
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Re: Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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01 Dec 2010, 00:16
(1) A=1 & A=6 ... insufficient (2) A=3 & A=14 ... insufficient (1+2) A+1 & A1 is a prime number ... A=4 & A=12 ... insufficient Answer is (e)
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Re: Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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01 Dec 2010, 20:04
NAD[/quote]
Possible values of A using S1: 1,2,4,6,10,12..... NOT SUFFICIENT Possible values of A using S2: 3,4,6,8,12......... NOT SUFFICIENT
Common values in both the lists: 4,6,12...........NOT SUFFICIENT
Answer: E[/quote]
Nice simple solution.....



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Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a [#permalink]
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27 Nov 2017, 14:24
Answer E
Statement 1and 2 are clearly insuff on their own.
A1, A, A+1 are consecutive integers, given than A1, A+1 are primes > A1 odd, A+1 odd, so A must be even.
if A1 is prime number other than 3, then A is divisible by 3 for sure.(since one of three consecutive integers will be divisible by 3, and A1 and A+1 are prime numbers not divisible by prime number 3, so A must be divisible by 3). if A1 =3, then A is NOT divisible by 3.
Not Sufficient > Answer (E)




Is A divisible by 3? (1) A+1 is a prime number (2) A1 is a
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