Out of the 30 students, 50% chose dogs and video games, so there are 30 * 0.50 = 15 students who chose dogs and video games.
10% chose dogs and movies, so there are 30 * 0.10 = 3 students who chose dogs and movies.
To find the total number of students who prefer dogs over cats, we need to add the students who chose dogs and video games to the students who chose dogs and movies. 
So, there are 15 + 3 = 18 students who prefer dogs over cats.
#### 18
The answer is: 18
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
During a unit on probability, a teacher surveys her class asking her students two questions.  The first question was whether they prefer dogs or cats, and the second question was whether they movies or video games.  Of the 30 students in her class, 50% chose dogs and video games as their two answers, while 10% chose dogs and movies as their two answers.  In total, how many students in this teacher's class prefer dogs over cats?

### Answer:
