A rectangle has a length of 5 inches and a width of 4 inches. What is the area, in square...

1. TRANSLATE the problem information

• Given information:
  • Rectangle with \(\mathrm{length = 5\ inches}\)
  • Rectangle with \(\mathrm{width = 4\ inches}\)
  • Need to find: area in square inches

2. INFER the approach

• Since we need the area of a rectangle, we use the area formula
• Rectangle \(\mathrm{area = length \times width}\)
• We have both dimensions, so we can calculate directly

3. Apply the formula

• \(\mathrm{Area = length \times width}\)
• \(\mathrm{Area = 5 \times 4 = 20\ square\ inches}\)

Answer: C) 20

Why Students Usually Falter on This Problem

Most Common Error Path:

Conceptual confusion about area vs. perimeter: Students mix up what "area" means and instead calculate the perimeter of the rectangle.

They think: "I need to find how much space around the rectangle" and calculate \(\mathrm{5 + 4 + 5 + 4 = 18}\), or sometimes just \(\mathrm{2(5 + 4) = 18}\).

This may lead them to select Choice B (18).

Second Most Common Error:

Weak INFER skill: Students recognize they need to use the given numbers but don't properly identify which operation to perform.

They might simply add the dimensions: \(\mathrm{5 + 4 = 9}\), thinking this gives them the "size" of the rectangle.

This may lead them to select Choice A (9).

The Bottom Line:

This problem tests whether students truly understand what "area" means (space inside a shape) versus "perimeter" (distance around a shape), and whether they can properly apply the rectangle area formula.