1. **Problem statement:** In a school, there are 3 classes of students taking Additional Mathematics. Class A has 42 students and class B has 40 students. Class A students constitute 35% of the total number of students taking Additional Mathematics. Find the number of students in class C. 2. **Formula and rules:** If class A students are 35% of the total, then total students $T$ satisfy $0.35T = 42$. 3. **Step-by-step solution:** - From $0.35T = 42$, solve for $T$: $$T = \frac{42}{0.35} = 120$$ - Total students in classes A, B, and C is $T = 120$. - Number of students in class C is: $$C = T - (A + B) = 120 - (42 + 40) = 120 - 82 = 38$$ 4. **Answer:** The number of students in class C is **38**.