5.4 · Part II
Supported Application · Guided Entry to Today's Problem
Area of Composite Figures · Composite Figure
- Decompose: Split the irregular shape into basic figures (rectangles, triangles, trapezoids)
- Calculate: Find the area of each individual sub-figure
- Combine: Add the areas together (or subtract if a piece is removed/cut out)
- Area of Composite Figures (Área de figuras compuestas) — The total space inside a figure made of basic shapes. Formula: A = A₁ + A₂ — add the parts (or subtract a missing piece).
- Composite Figure (Figura compuesta) — A shape made by putting two or more simple shapes together.
- Decompose (Descomponer) — To break a shape into smaller, simpler shapes.
- Add (Sumar) — Add up the areas of the smaller shapes to get the total.
- Subtract (Restar) — Take away the area of a missing piece from a bigger shape.
- Formula (Fórmula) — A math rule written with symbols.
- A common mistake in Area of Composite Figures is adding every piece even when a piece has been cut out of the figure. For a 10 ft by 8 ft rectangle with a 3 ft by 2 ft rectangular notch cut from one corner, students compute the full rectangle 10 × 8 = 80 sq ft and stop, or they add the notch instead of removing it (80 + 6 = 86 sq ft) instead of subtracting it: 80 − (3 × 2) = 80 − 6 = 74 sq ft. Before submitting, check whether each piece is part of the figure (add it) or missing from the figure (subtract it).
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1 MULTIPLE CHOICE
When should you subtract areas instead of adding them to find the area of a composite figure?
- AWhen a piece is cut out or removed from a larger shape
- BWhen the shapes overlap
- CWhen one shape is larger than the other
- DAlways subtract — never add
✏️ Workspace & Solution Steps -
2 MULTIPLE CHOICE
(Lesson 5.9) A regular hexagon is divided into 6 equal triangles from the center. Each triangle has a base of 6 ft and a height of 5.2 ft. What is the area of one triangle?
- A15.6 sq ft
- B31.2 sq ft
- C11.2 sq ft
- D15.6 ft
FormulaPut the numbers inWork it outAnswer with its unit- 1Name itWhich measure is asked?
- 2Write the formulaBefore any numbers.
- 3SubstituteMatch each letter.
- 4Unitunits, sq units, or cubic?
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3 MULTIPLE CHOICE
(Lesson 5.9) Using the triangle from the previous question, what is the total area of the hexagonal skylight?
- A93.6 sq ft
- B15.6 sq ft
- C187.2 sq ft
- D62.4 sq ft
FormulaPut the numbers inWork it outAnswer with its unit- 1Name itWhich measure is asked?
- 2Write the formulaBefore any numbers.
- 3SubstituteMatch each letter.
- 4Unitunits, sq units, or cubic?
Writing Task: Justify why your mathematical solution is accurate and complete.
5.4 · Part II
On-Level Application · Standard Rigor
Area of Composite Figures · Composite Figure
- Decompose: Split the irregular shape into basic figures (rectangles, triangles, trapezoids)
- Calculate: Find the area of each individual sub-figure
- Combine: Add the areas together (or subtract if a piece is removed/cut out)
- Area of Composite Figures (Área de figuras compuestas) — The total space inside a figure made of basic shapes. Formula: A = A₁ + A₂ — add the parts (or subtract a missing piece).
- Composite Figure (Figura compuesta) — A shape made by putting two or more simple shapes together.
- Decompose (Descomponer) — To break a shape into smaller, simpler shapes.
- Add (Sumar) — Add up the areas of the smaller shapes to get the total.
- Subtract (Restar) — Take away the area of a missing piece from a bigger shape.
- Formula (Fórmula) — A math rule written with symbols.
- A common mistake in Area of Composite Figures is adding every piece even when a piece has been cut out of the figure. For a 10 ft by 8 ft rectangle with a 3 ft by 2 ft rectangular notch cut from one corner, students compute the full rectangle 10 × 8 = 80 sq ft and stop, or they add the notch instead of removing it (80 + 6 = 86 sq ft) instead of subtracting it: 80 − (3 × 2) = 80 − 6 = 74 sq ft. Before submitting, check whether each piece is part of the figure (add it) or missing from the figure (subtract it).
-
1 MULTIPLE CHOICE
A 7 ft by 5 ft rectangle has a triangle (base 7 ft, height 4 ft) on top. Add the two areas. What is the total area?
- A49 sq ft
- B35 sq ft
- C14 sq ft
- D63 sq ft
FormulaPut the numbers inWork it outAnswer with its unit -
2 MULTIPLE CHOICE
Plan 2 — L-shaped lobby: decompose the L into two rectangles, one 9 ft by 6 ft and one 7 ft by 3 ft, then ADD. What is the total floor area?
- A75 sq ft
- B63 sq ft
- C54 sq ft
- D21 sq ft
FormulaPut the numbers inWork it outAnswer with its unit -
3 MULTIPLE CHOICE
Plan 4 — Design studio: the floor is a 16 ft by 12 ft rectangle, but a 5 ft by 4 ft storage closet is cut out of one corner. Find the usable floor area.
- A172 sq ft
- B192 sq ft
- C212 sq ft
- D20 sq ft
FormulaPut the numbers inWork it outAnswer with its unit
Writing Task: Justify why your mathematical solution is accurate and complete.
5.4 · Part II
Extension & Non-Routine Application
Area of Composite Figures · Composite Figure
- Decompose: Split the irregular shape into basic figures (rectangles, triangles, trapezoids)
- Calculate: Find the area of each individual sub-figure
- Combine: Add the areas together (or subtract if a piece is removed/cut out)
- Area of Composite Figures (Área de figuras compuestas) — The total space inside a figure made of basic shapes. Formula: A = A₁ + A₂ — add the parts (or subtract a missing piece).
- Composite Figure (Figura compuesta) — A shape made by putting two or more simple shapes together.
- Decompose (Descomponer) — To break a shape into smaller, simpler shapes.
- Add (Sumar) — Add up the areas of the smaller shapes to get the total.
- Subtract (Restar) — Take away the area of a missing piece from a bigger shape.
- Formula (Fórmula) — A math rule written with symbols.
- A common mistake in Area of Composite Figures is adding every piece even when a piece has been cut out of the figure. For a 10 ft by 8 ft rectangle with a 3 ft by 2 ft rectangular notch cut from one corner, students compute the full rectangle 10 × 8 = 80 sq ft and stop, or they add the notch instead of removing it (80 + 6 = 86 sq ft) instead of subtracting it: 80 − (3 × 2) = 80 − 6 = 74 sq ft. Before submitting, check whether each piece is part of the figure (add it) or missing from the figure (subtract it).
-
1 MULTIPLE CHOICE
An L-shaped room splits into two rectangles: one is 12 feet by 8 feet, the other is 6 feet by 5 feet. What is the total floor area?
- A126 square feet
- B96 square feet
- C30 square feet
- D62 square feet
FormulaPut the numbers inWork it outAnswer with its unit
Writing Task: Justify why your mathematical solution is accurate and complete.