If 75% of the cars have valid tickets, then the number of cars with valid tickets is 300 * 0.75 = 225 cars.
If 1/5th of that number have permanent parking passes, then the number of cars with permanent parking passes is 225 * (1/5) = 45 cars.
Therefore, the number of cars in the parking lot that tried to park without paying is 300 - 225 - 45 = 30 cars.
#### 30
The answer is: 30
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
If there are 300 cars in the parking lot and 75% of them have valid tickets, and 1/5th of that number have permanent parking passes, how many cars in the parking lot tried to park without paying?

### Answer:
