1. **State the problem:** Calculate the area of a triangle with base 20 cm and height 12 cm. 2. **Formula:** The area $A$ of a triangle is given by the formula: $$A = \frac{1}{2} \times \text{base} \times \text{height}$$ 3. **Apply the formula:** Substitute base = 20 cm and height = 12 cm: $$A = \frac{1}{2} \times 20 \times 12$$ 4. **Simplify:** $$A = \frac{1}{2} \times 240$$ $$A = \cancel{\frac{1}{2}} \times \cancel{240} 120$$ 5. **Final answer:** The area of the triangle is $120$ square centimeters.