Subject
Quantitative Aptitude
Topic
Number
If x is a prime such that (x2 + 7) is also a prime, then x can have
If x is a prime such that (x2 + 7) is also a prime, then x can have
ক)
2 valuesখ)
1 valueগ)
More than 2 valuesঘ)
None of theseঙ)
can’t be determinedExplanation
We know that, Square of an odd number is an odd number itself and sum of two odd numbers is an even number. Also the smallest and only even prime number is 2. Now, (x2 + 7) > 2 will be a prime number only when it is an odd number and thus x must be an even number for (x2 + 7) to be odd. Also since x itself is a prime number thus the only possible value of x that satisfies it to be prime and even both is 2. 22 + 7 = 11 is a prime number. ∴ x can have only one value i.e. ‘2’ for (x2 + 7) to be a prime number.Related questions
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