Which one of the following expressions has an even integer value for all integers a and c ?
A. 8a + 2ac
B. 3a + 3c
C. 2a + c
D. a + 2c
The correct answer is: A. 8a + 2ac
How do you get to this answer: It is divisible by 2, 8a + 2ac = 2(4a + ac), and 4a + ac is an integer because a and c are integers.