Discussion

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 -.

Answer: D

Among the first 20 natural numbers:

\[ \text{even} = 10, \qquad \text{prime} = 8 \ (2, 3, 5, 7, 11, 13, 17, 19) \]

Only 2 is both, so

\[ 10 + 8 - 1 = 17 \quad\Longrightarrow\quad P = \frac{17}{20} \]

2 is the only even prime, which is exactly why the overlap here is a single number.

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