Each Ferris wheel in paradise park has 19 seats. Each seat in a Ferris wheel can hold 15 people. How many people can ride 20 Ferris wheels at the same time?
Let's denote the number of Ferris wheels by n. Then the number of seats in n Ferris wheels is n*19. 

The number of people that can ride n Ferris wheels at the same time is 

n*19*15. 

Therefore the answer (numeric) is: 

n*19*15 = 20*19*15 = 5700