Read the problem carefully. This problem is very straightforward, so there are no circumstances to take special note of.
Identify the bottom line. a = ?
Assess your options. This problem deals with absolute value. The absolute value of a number is its distance from zero on the number line. Absolute value is shown using two parallel lines, like the ones you see in the problem above. Let’s look at a quick example of absolute value before moving on. Say that the absolute value of x is 4. That means that x can be either 4 or -4 because both numbers are 4 away from zero on the number line. Written out mathematically, that information looks like this:
To solve this problem, you could plug in all the answer choices and see which one works, or you could use your understanding of absolute value. We will look at the latter method below.
Attack the problem. If the absolute value of a + 7 is 13, then a + 7 can be equal to either 13 or -13. Solve for a in both situations.
a + 7 = 13
- 7 -7
a = 6
a + 7 = -13
- 7 -7
a = -20
-20 is one of the answer choices, so that must be the correct answer.
Loop back. Did we solve for the bottom line? Yes.
The correct answer is A.