Final answer:
To find the percentage decrease in volume of a rectangular parallelepiped, calculate the new volume after decreasing the dimensions and then find the percentage decrease.
Step-by-step explanation:
To find the percentage decrease in volume, we need to first calculate the new volume after decreasing the dimensions of the rectangular parallelepiped. Let's assume the initial length, width, and height of the parallelepiped are L, W, and H respectively. After decreasing the length by 25%, the new length will be 0.75L. Similarly, the new width and height will be 0.8W and 0.8H respectively.
The new volume is calculated by multiplying the new dimensions: Volume' = (0.75L) * (0.8W) * (0.8H).
Now, we can calculate the percentage decrease in volume by subtracting the new volume from the initial volume, dividing it by the initial volume, and multiplying by 100: Percentage decrease = (Volume - Volume') / Volume * 100.
Substituting the values and simplifying the expression will give you the final answer.