A father is buying sand to fill his son's new sandbox, but he is worried that the sand will be too heavy for his car. The sandbox is square, with each side being 40 inches long. If a 30-pound bag of sand is enough to fill 80 square inches of the sandbox to an adequate depth, how many pounds of sand are needed to fill the box completely? Give me reasons, before answering the question
The sandbox has an area of 40 * 40 = 1600 square inches. To fill this area, 1600 / 80 = 20 bags of sand are needed. Then, the weight of these bags is 20 * 30 = 600 pounds. So the final answer is 600.