A rectangle has a perimeter of 50 inches and a width of 10 inches. What is its length?

1. Start from the perimeter formula: P equals 2L plus 2W. 2. Substitute the known values: 50 equals 2L plus 2 times 10, so 50 equals 2L plus 20. 3. Subtract 20 from both sides: 30 equals 2L. 4. Divide both sides by 2: L equals 15. 5. The length of the rectangle is 15 inches. 6. Forgetting to double the width before subtracting, and subtracting only 10 from 50, gives 40 for 2L and then 20 for L, well above the true length. 7. Treating half the perimeter as the length outright, 50 divided by 2, gives 25 inches and ignores that the width must be subtracted first. _Source: OpenStax Prealgebra (CC BY 4.0), Ch 9 "Math Models and Geometry", section 9.4 Use Properties of Rectangles, Triangles, and Trapezoids_