To find the volume of a pyramid, you can use the formula:
\[ \text{Volume} = \frac{1}{3} \times \text{Base Area} \times \text{Height} \]
First, we need to calculate the base area of the pyramid. The base is a rectangle, so the area can be calculated as:
\[ \text{Base Area} = \text{Length} \times \text{Width} = 8 , \text{inches} \times 12 , \text{inches} = 96 , \text{square inches} \]
Now, we can use the height of the pyramid, which is given as 20 inches.
Now, substituting the values into the volume formula:
\[ \text{Volume} = \frac{1}{3} \times 96 , \text{square inches} \times 20 , \text{inches} \]
Calculating step by step:
- Multiply the base area by the height:
\[ 96 \times 20 = 1920 , \text{cubic inches} \]
- Now, divide by 3 to find the volume:
\[ \text{Volume} = \frac{1920}{3} = 640 , \text{cubic inches} \]
Thus, the volume of Cecilia's model pyramid is
\[ \boxed{640} , \text{cubic inches} \]