The correct answer is (c).
The number of people who read at least two newspapers is the sum of the number of people who read both newspapers, the number of people who read only newspaper A, and the number of people who read only newspaper B. This can be calculated using the following formula:
$n(A \cup B) = n(A) + n(B) – n(A \cap B)$
where $n(A)$ is the number of people who read newspaper A, $n(B)$ is the number of people who read newspaper B, and $n(A \cap B)$ is the number of people who read both newspapers.
In this case, we know that $n(A) = 20$, $n(B) = 30$, and $n(A \cap B) = 10$. Substituting these values into the formula, we get:
$n(A \cup B) = 20 + 30 – 10 = 40$
Therefore, we can expect 40 people in a population of 10,000 to be reading at least two newspapers.
Option (a) is incorrect because it is the total number of people who read at least one newspaper. Option (b) is incorrect because it is the sum of the number of people who read only newspaper A and the number of people who read only newspaper B. Option (d) is incorrect because it is the number of people who read both newspapers.