ACT Question of the Day #37

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.