A number is randomly chosen from the first 20 natural numbers. What is the probability that the selected number is either even or prime?

Explanation

The total number of outcomes is 20. There are 10 even numbers and 8 prime numbers within the first 20 natural numbers. Since 2 is both even and prime, it is counted twice. Using the formula for the union of two events: P(even or prime) = P(even) + P(prime) - P(both) = 10/20 + 8/20 - 1/20 = 17/20.