the integer K?

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the integer K?

by sanju09 » Thu Sep 16, 2010 10:19 pm
What is the value of the integer K?

[1] K is a prime number between 40 and 50.

[2] The integer (K + 1) is divisible by exactly two different prime numbers.


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by sumit.sinha » Sat Sep 18, 2010 5:36 am
sanju09 wrote:What is the value of the integer K?

[1] K is a prime number between 40 and 50.

[2] The integer (K + 1) is divisible by exactly two different prime numbers.


[spoiler]Source: https://www.west.net/~stewart/gmat[/spoiler]
(1) K = 41, 43 or 47 NOT SUFFICIENT
(2) K =5 or 9.
Because 5+1 = 6 is divisible by exactly two different prime numbers 2 and 3.
Note: it is given (K + 1) is divisible by exactly two different prime numbers and NOT (K + 1) is ONLY divisible by exactly two different prime numbers. so there maybe other non-prime factors but we are not concerned about them.
and 9 +1 =10 is divisible by exactly two different prime numbers 2 and 5.
NOT SUFFICIENT

(1) ans (2) together - K = 43 or 47
Because if K = 41, K +1 = 42 is divisible by three different prime factors 2,3 and 7
if K = 43, K +1 = 44 is divisible by exactly two different prime factors 2 and 11
if K = 47, K +1 = 48 is divisible by exactly two different prime factors 2 and 3
NOT SUFFICIENT

CORRECT ANSWER (E)
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by puneetdua » Sat Sep 18, 2010 8:46 am
Should be E.
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