To find the volume of a rectangular prism, we multiply its length, width, and height. In this case, we are given the length as 5cm and the height as 20cm, but we are not given the width. Let's assume the width is 10cm (although it could be any value as long as it is consistent with the shape of a rectangular prism).
Volume = length x width x height
Volume = 5cm x 10cm x 20cm
Volume = 1000 cubic centimeters
Rounding to the nearest tenth of a cubic centimeter, we get:
Volume ≈ 1000.0 cubic centimeters
Therefore, the volume of the rectangular prism is approximately 1000.0 cubic centimeters.