Step 1: Understanding the Question:
This is a standard set theory problem. We are given the total number of people, the number of people in two individual sets, and the number of people outside both sets. We need to find the intersection of the two sets.
Step 2: Key Formula or Approach:
Use the principle of inclusion-exclusion for two sets:
\[ n(A \cup B) = n(A) + n(B) - n(A \cap B) \]
Where \(n(A \cup B)\) is the number of people who studied at least one of the subjects, which can be found by subtracting the "neither" group from the total group.
Step 3: Detailed Explanation:
Let \(F\) be the set of people who studied French, and \(S\) be the set of people who studied Spanish.
Total number of people in the group \(= 25\).
Number of people who studied neither \(= 8\).
Number of people who studied at least one language \(n(F \cup S) = 25 - 8 = 17\).
We are given:
\(n(F) = 10\)
\(n(S) = 11\)
Substitute these values into the inclusion-exclusion formula:
\[ 17 = 10 + 11 - n(F \cap S) \]
\[ 17 = 21 - n(F \cap S) \]
\[ n(F \cap S) = 21 - 17 = 4 \]
Therefore, \(4\) people studied both French and Spanish.
Step 4: Final Answer:
The number of people who studied both is \(4\).