1. **State the problem:** We have a parallelogram with base 10 cm and height 4 cm, cut into three pieces: two right triangles and one rectangle. We want to rearrange these pieces to form a rectangle and find its area. 2. **Formula and rules:** The area of a parallelogram is given by $$\text{Area} = \text{base} \times \text{height}$$ 3. **Rearrangement explanation:** When the three pieces (two right triangles and one rectangle) are rearranged side by side, they form a rectangle with the same base and height as the original parallelogram. 4. **Calculate the area of the rectangle:** $$\text{Area} = 10 \times 4 = 40$$ 5. **Conclusion:** The area of the rectangle formed by rearranging the pieces of the parallelogram is 40 square centimeters.