Math Problem Statement

Find the perimeter and total area of the composite shape consisting of a trapezoid and a semicircle. All measurements are given in inches. Use π = 3.14 in any formulas used.

Solution

The composite shape in the image consists of two distinct parts:

  1. A trapezoid with the following dimensions:

    • Bottom base: 20 inches
    • Top base: 8 inches
    • Height: 8 inches
    • The slant height of each side of the trapezoid is 10 inches.
  2. A semicircle placed on top of the trapezoid:

    • The diameter of the semicircle is 8 inches (since it matches the top base of the trapezoid).
    • Therefore, the radius of the semicircle is 82=4\frac{8}{2} = 4 inches.

Step 1: Perimeter Calculation

The perimeter consists of:

  • The perimeter of the trapezoid (two slanted sides and the bottom base).
  • The perimeter of the semicircle (its curved part).

1.1 Trapezoid's perimeter:

  • Bottom base = 20 inches
  • The two slanted sides = 10 inches each

The straight top edge is covered by the diameter of the semicircle, so we exclude it from the perimeter. The perimeter contribution from the trapezoid is: Ptrapezoid=20+10+10=40inchesP_{\text{trapezoid}} = 20 + 10 + 10 = 40 \, \text{inches}

1.2 Semicircle's perimeter:

The curved part of the semicircle’s perimeter is half of the circumference of a full circle: Csemicircle=12×2πr=πr=3.14×4=12.56inchesC_{\text{semicircle}} = \frac{1}{2} \times 2 \pi r = \pi r = 3.14 \times 4 = 12.56 \, \text{inches}

Thus, the total perimeter of the shape is: Ptotal=Ptrapezoid+Csemicircle=40+12.56=52.56inchesP_{\text{total}} = P_{\text{trapezoid}} + C_{\text{semicircle}} = 40 + 12.56 = 52.56 \, \text{inches}

Step 2: Area Calculation

The total area consists of the area of the trapezoid and the area of the semicircle.

2.1 Trapezoid's area:

The area of a trapezoid is given by the formula: Atrapezoid=12×(b1+b2)×hA_{\text{trapezoid}} = \frac{1}{2} \times (b_1 + b_2) \times h Where:

  • b1=20b_1 = 20 inches (bottom base)
  • b2=8b_2 = 8 inches (top base)
  • h=8h = 8 inches (height)

Substituting these values: Atrapezoid=12×(20+8)×8=12×28×8=112square inchesA_{\text{trapezoid}} = \frac{1}{2} \times (20 + 8) \times 8 = \frac{1}{2} \times 28 \times 8 = 112 \, \text{square inches}

2.2 Semicircle's area:

The area of a semicircle is half the area of a full circle: Asemicircle=12×πr2=12×3.14×42=12×3.14×16=25.12square inchesA_{\text{semicircle}} = \frac{1}{2} \times \pi r^2 = \frac{1}{2} \times 3.14 \times 4^2 = \frac{1}{2} \times 3.14 \times 16 = 25.12 \, \text{square inches}

2.3 Total area:

The total area is the sum of the areas of the trapezoid and the semicircle: Atotal=Atrapezoid+Asemicircle=112+25.12=137.12square inchesA_{\text{total}} = A_{\text{trapezoid}} + A_{\text{semicircle}} = 112 + 25.12 = 137.12 \, \text{square inches}

Final Results:

  • Perimeter: 52.56 inches
  • Total area: 137.12 square inches

Would you like further details or have any questions? Here are 5 related questions to expand your understanding:

  1. How would the perimeter change if the radius of the semicircle doubled?
  2. What is the formula for the perimeter of a full circle and how would it be applied here?
  3. How do you calculate the area of a trapezoid if the bases are not parallel?
  4. If the trapezoid had different slant heights, how would that affect the perimeter calculation?
  5. What if the shape were a full circle instead of a semicircle—how would the area change?

Tip: When working with composite shapes, always calculate areas and perimeters for individual parts before combining them for accurate results.

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Math Problem Analysis

Mathematical Concepts

Geometry
Perimeter Calculation
Area Calculation
Composite Shapes

Formulas

Perimeter of a trapezoid: P_trapezoid = a + b + c (excluding the top base covered by the semicircle)
Perimeter of a semicircle: C_semicircle = π * r
Area of a trapezoid: A_trapezoid = 1/2 * (b1 + b2) * height
Area of a semicircle: A_semicircle = 1/2 * π * r^2

Theorems

Formula for circumference and area of a circle
Area of a trapezoid

Suitable Grade Level

Grades 8-10