The probability shows that the expected number of cards given to people whose age matches the number on the card is 1.
How to compute the expected value?
From the information, a set of 1000 cards, numbered 1 through 1000, are distributed among 1000 people.
Let x be the random variable that's equal to the number of people who get a card.
Since we are looking for the expected value, this will be:
= E(X1 + X2 + .... X1000)
= 1