Question

what does {x | x < 13 or x > 15} represent?
all numbers less than 13 or greater than 15
all numbers greater than 13 or less than 15
all numbers less than or equal to 13 or greater than 15
all numbers less than or equal to 13 or greater than or equal to 15

Explanation:

Step1: Interpret set - builder notation

The set $\{x|x < 13\text{ or }x>15\}$ means for each element $x$ in the set, $x$ satisfies either $x < 13$ or $x>15$.
This directly translates to all numbers less than 13 or greater than 15.

Answer:

all numbers less than 13 or greater than 15