There are 30 students in total, and 18 of them own at least one pet.

The fraction of students who own pets is:

$\frac{18}{30}$

To simplify this fraction, divide both the numerator and the denominator by their greatest common divisor (GCD), which is 6:

$\frac{18 \div 6}{30 \div 6} = \frac{3}{5}$

So, the fraction of the class that owns pets is:

$\frac{3}{5}$

Would you like more details or have any questions?

Here are 5 related questions for further exploration:

1. What fraction of the class does not own a pet?
2. If 5 more students got pets, what fraction would own pets then?
3. What is the decimal representation of the fraction $\frac{3}{5}$?
4. If only half of the students with pets own dogs, how many students own dogs?
5. What percentage of the class owns pets?

Tip: To simplify fractions, always look for the greatest common divisor (GCD) of both the numerator and the denominator.