Final answer:
The dimensions of Sally's painting are 12 inches by 40 inches, since the area is 480 square inches and the length is 1 1/5 times the width. By testing all the given options, only 12 inches by 40 inches satisfies both conditions.
Step-by-step explanation:
The question is about determining the dimensions of Sally's painting, given that its area is 480 square inches and the length is 1 1/5 times its width. Solving this kind of problem involves understanding the relationship between length and width for rectangles and how to compute areas. To find the correct dimensions among the options given, we look for a pair of numbers where the length is 1 1/5 times the width and the product of the two numbers equals 480 square inches. For example, with Option A, 20 inches by 24 inches, if we multiply these dimensions (20x24), we get an area of 480 square inches. However, 24 is not 1 1/5 times 20, so Option A is incorrect. By testing each option, we find that Option B, 12 inches by 40 inches, is the correct answer because 40 is 1 1/5 times 12, and the product of 12 and 40 is indeed 480 square inches.