Out of first 20 natural numbers, one number is selected at random

Out of first 20 natural numbers, one number is selected at random. The probability that it is either an even number or a prime number is ?

This problem repeats another one in the library (at most with different numbers), so it's left out of browsing.

AQuA-RAT — Algebra Question Answering with Rationales (Ling et al., DeepMind, 2017) · train #1447