If p and q are different prime numbers and pq/2 is also a prime number, then p + q is
(A) an odd number
(B) an even number
(C) a prime number
(D) a negative number
(E) not a prime number
Sunday, April 29, 2007
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7 comments:
E
e
i think E is wrong
what if p=2 and q=3
pq/2 =3
p+q=5 … a prime number
i prefer A,
since pq/2 s prime refers either p or q is 2.
then p+q=2+q
where q is odd.
so asum will be always odd.
what is the answer?
Answer is A
madhur is right.
A
Since pq/2 is prime, it is an integer. Hence, either p or q must be even; otherwise, the 2 would not
cancel and pq/2 would be a fraction. The only even prime number is 2. Hence, either p or q, but not both,
must be 2. The other one is an odd prime number. Now, the sum of an even number and an odd number is
an odd number. The answer is (A).
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