Answer: 12

The correct answer is **B (12)** because the degrees of freedom for a chi-square test of independence in a contingency table are calculated as \((r - 1)(c - 1)\), where \(r\) is the number of rows and \(c\) is the number of columns. Here, \(r = 5\) and \(c = 4\), so the degrees of freedom are \((5 - 1)(4 - 1) = 4 \times 3 = 12\). - **Option A (7)** is incorrect as it results from using the formula \(r + c - 2\), which is not applicable here. - **Option C (20)** is incorrect as it arises from omitting the \(-1\) adjustment, leading to \(r \times c = 5 \times 4 = 20\), which is not the correct calculation.

Author: LeetQuiz Editorial Team