If the sum of a set of 7 different positive prime numbers is an even number, which of the following prime numbers must be in the set?
Choose the correct choice:
A) 2  B) 3  C) 5  D) 7  E) 11
All prime numbers apart from 2 are odd.   Even + Even = Even   Odd + Even = Odd   Odd + Odd = Even   We are given 7 different prime numbers, whose sum is even   If we include 2, we will have 6 odd prime numbers and one even.   This sum would be even   If we exclude 2, we will have 7 odd numbers.   This sum would be odd   Hence 2 is included.   Option 2
<result>A</result>
If the sum of a set of 7 different positive prime numbers is an even number, which of the following prime numbers must be in the set?