1. **State the problem:** You have four classes, each worth 25% of your overall grade. You scored 85% in three classes and 50% in one class. We need to find your overall mark. 2. **Formula:** The overall grade is the weighted average of the individual grades. Since each class is worth 25%, the formula is: $$\text{Overall Grade} = 0.25 \times G_1 + 0.25 \times G_2 + 0.25 \times G_3 + 0.25 \times G_4$$ where $G_i$ are the grades for each class. 3. **Substitute the values:** $$\text{Overall Grade} = 0.25 \times 85 + 0.25 \times 85 + 0.25 \times 85 + 0.25 \times 50$$ 4. **Calculate each term:** $$0.25 \times 85 = 21.25$$ $$0.25 \times 50 = 12.5$$ 5. **Sum the terms:** $$21.25 + 21.25 + 21.25 + 12.5 = 76.25$$ 6. **Final answer:** Your overall mark is **76.25%**.