If x and y are integers, is x(y+1) an even number?
1). x, and y are prime numbers.
2). y>7
1) e.g. x = 2, y = 5 --> 2(5+1) = 12 --> EVEN
x = 3, y = 2 --> 3(2+1) = 9 --> ODD.
2) y>7, y could 8, 9, 10, 11, 12...... and so on.
let's say y=8 and x = 2 --> 2(8+1) = 18 --> EVEN
OR y = 9 and x = 2 --> 2(9+1) -->20
BUT who's to say that x can't be odd? x =3, y = 8 --> 3(9) = 27 ODD.
OR x = 3, y = 9 --> 3(10) = 30 EVEN.
obviously the both alone are inefficient.
TOGETHER, if x and y are prime numbers AND y is > 7, then is x(y+1) even?
let's say x = 2 (even prime) and y = 11 (odd prime number > 7), then 2(11+1) = 24 EVEN.
OR say x = 3 (odd) and y = 13 (odd), then 3(13+1) = 3(14) = 42. EVEN.
SO we learned that: ODD * EVEN = EVEN, or EVEN*EVEN = EVEN
Answer should be C. Hope this helps.
