Need cardboard to build a box 10 in long, 9 in wide and 7 in high. If 500 square inches of cardboard are purchased, how much is left over?
To calculate the total surface area of the box, we need to find the surface area of each of the six sides and then add them together.
Surface area of the bottom and top sides:
10 in x 9 in = 90 square inches each
2 sides x 90 square inches = 180 square inches
Surface area of the front and back sides:
10 in x 7 in = 70 square inches each
2 sides x 70 square inches = 140 square inches
Surface area of the left and right sides:
9 in x 7 in = 63 square inches each
2 sides x 63 square inches = 126 square inches
Total surface area = 180 + 140 + 126 = 446 square inches
Thus, if 500 square inches of cardboard are purchased and 446 square inches are used to build the box, then 500 - 446 = 54 square inches are left over.