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Given that K=(N+2)(N-2) and according to statement 1 K is the product of two prime numbers then (N+2) = prime and (N-2)= prime. I interpret that to mean that N is two intervals away from 2 prime numbers, the only example I could think of to fit this description would be (5+2)(5-2) (7)(3) = 21. What other prime numbers would fit this description? Where am I going wrong on this statement? Should I just assume that there will be more prime numbers to fit this premise? Am I supposed to remember prime numbers past 100? I see the second statement says that K<100 and I realize that the statement is clearly insufficient on its own so I selected "A."
OA is "E"
Can someone explain where I am going wrong with this one?
Re: If k = (n + 2)(n - 2), where n is an integer value greater
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23 Feb 2014, 14:49
7
4
msbandi4321 wrote:
If k = (n + 2)(n - 2), where n is an integer value greater than 2, what is the value of k?
(1) k is the product of two primes (2) k < 100
My approach: Given that K=(N+2)(N-2) and according to statement 1 K is the product of two prime numbers then (N+2) = prime and (N-2)= prime. I interpret that to mean that N is two intervals away from 2 prime numbers, the only example I could think of to fit this description would be (5+2)(5-2) (7)(3) = 21. What other prime numbers would fit this description? Where am I going wrong on this statement? Should I just assume that there will be more prime numbers to fit this premise? Am I supposed to remember prime numbers past 100? I see the second statement says that K<100 and I realize that the statement is clearly insufficient on its own so I selected "A."
OA is "E"
Can someone explain where I am going wrong with this one?
If k = (n + 2)(n - 2), where n is an integer value greater
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10 Sep 2018, 01:37
Bunuel wrote:
msbandi4321 wrote:
If k = (n + 2)(n - 2), where n is an integer value greater than 2, what is the value of k?
(1) k is the product of two primes (2) k < 100
My approach: Given that K=(N+2)(N-2) and according to statement 1 K is the product of two prime numbers then (N+2) = prime and (N-2)= prime. I interpret that to mean that N is two intervals away from 2 prime numbers, the only example I could think of to fit this description would be (5+2)(5-2) (7)(3) = 21. What other prime numbers would fit this description? Where am I going wrong on this statement? Should I just assume that there will be more prime numbers to fit this premise? Am I supposed to remember prime numbers past 100? I see the second statement says that K<100 and I realize that the statement is clearly insufficient on its own so I selected "A."
OA is "E"
Can someone explain where I am going wrong with this one?
Thanks in advance.
What about 7*11 = 77?
Thanks. So is the approach here to name n 1 through 9 and see what K we get? or rather it is see that (2) provides info on K < 100 therefore go back to (1) and check till 100?
Given that K=(N+2)(N-2) and according to statement 1 K is the product of two prime numbers then (N+2) = prime and (N-2)= prime. I interpret that to mean that N is two intervals away from 2 prime numbers, the only example I could think of to fit this description would be (5+2)(5-2) (7)(3) = 21. What other prime numbers would fit this description? Where am I going wrong on this statement? Should I just assume that there will be more prime numbers to fit this premise? Am I supposed to remember prime numbers past 100? I see the second statement says that K<100 and I realize that the statement is clearly insufficient on its own so I selected "A."
OA is "E"
Can someone explain where I am going wrong with this one?
Thanks in advance.
OA: E
Given: \(k = (n + 2)(n - 2)\) and \(n>2\)
(1) \(k\) is the product of two primes
Difference between Two primes would be \((n+2)-(n-2)= n+2-n+2=4\), Primes number can \({3,7};{7,11};\)..... as there is no unique value of \(k\) , \(k\) can be \(21,77\) or ...... So Statement \(1\) alone is not sufficient.
(2) \(k < 100\)
\(k\) can be \(1,2,3,4\)............... There is no unique value of \(k\) , so Statement \(2\) alone is not sufficient.
Combining (1) and (2), we get \(k\) can be 21 or 77, so combining (1) and (2) also is insufficient to give unique value of \(k\)
_________________
What is the best approach to solving this problem? I get the solution but is there any approach other than assuming values of n starting from 1? In such cases, ita difficult to know till what value of n should we test till. I tested it till 8 and then guessed A would be correct
Re: If k = (n + 2)(n - 2), where n is an integer value greater
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12 May 2019, 14:52
jyotsnamahajan wrote:
What is the best approach to solving this problem? I get the solution but is there any approach other than assuming values of n starting from 1? In such cases, ita difficult to know till what value of n should we test till. I tested it till 8 and then guessed A would be correct
But you only have to test some values (lets say 2) to reach at multiple values to be the answer, then its insuff
For ex
1) says that n>2 then: n= 5 we have 7*3= 21 and n=9 we have 11*7= 77
2 different values that satisfy the condition, hence insuff
2) k<100 ns
1+2) still it could be 21 or 77 (both k<100) hence insuff --> E
If k = (n + 2)(n - 2), where n is an integer value greater
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24 May 2019, 11:36
Given: k = (n+2)(n-2) = n²-4, int n > 2 Question: k = ?
(1) k is the product of two primes I thought about listing out the prime numbers to 100 and seeing what fit (n+2)(n-2) but decided this would take way too long. Instead I made a chart using n²-4 to check: n | n² | - 4 | product of 2 pn? 3 | 9 | 5 | No 4 | 16 | 12 | No 5 | 25 | 21 | YES --- 3*7 6 | 36 | 32 | No 7 | 49 | 45 | No 8 | 64 | 60 | No 9 | 81 | 77 | YES --- 7*11
2 Answers, can't determine value of k, insufficient.
(2) k < 100 Totally useless in determining what k actually is. Insufficient.
(3) Combining together doesn't help because we still have 2 possibilities for k that will satisfy both statements.
gmatclubot
If k = (n + 2)(n - 2), where n is an integer value greater
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24 May 2019, 11:36
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67% (01:50) correct 
