Start here

You did these with your group. Now do them on your own — the model above is yours to copy.

1. 1

   Same stepsFinish what the group started. Use the model above, step for step.

   Try it together — then prove it: An L-shape is made of a 5 ft by 4 ft rectangle and a 3 ft by 2 ft rectangle. Find its area. Find the area of each rectangle. (5 × 4 = 20 and 3 × 2 = 6) What is the total area? (20 + 6 = 26 square feet) Why do we add here, and not subtract? (The two rectangles are joined. Nothing is cut out, so each piece adds more area.)

   Show your work
2. 2

   Warm restartIn the formula A = ½(b₁ + b₂) × h, what do b₁ and b₂ stand for?

   1. AThe two slanted sides
   2. BThe base and the height
   3. CThe perimeter and the height
   4. DThe two parallel sides

   How do you know?
3. 3

   Warm restartWhat is the area of a trapezoid with bases 6 cm and 10 cm and height 4 cm?

   1. A20 square cm
   2. B32 square cm
   3. C64 square cm
   4. D240 square cm

   How do you know?
4. 4

   Warm restartWhat is the area of a trapezoid with bases 5 cm and 9 cm and height 6 cm?

   1. A20 square cm
   2. B42 square cm
   3. C84 square cm
   4. D270 square cm

   How do you know?

You answered these out loud. Now write them.

Answer, then say how you know — the reason is the part that counts.

1. 5

   Think it throughWhat is the area of the top of the T?

   1. A18 sq ft
   2. B36 sq ft
   3. C56 sq ft
   4. D60 sq ft

   Why is that the answer?
2. 6

   Think it throughWhat is the total area of the T-shaped room?

   1. A96 sq ft
   2. B104 sq ft
   3. C116 sq ft
   4. D840 sq ft

   How do you know? Give a second reason as well.
3. 7

   Think it throughWhat will the carpet cost?

   1. A$116
   2. B$300
   3. C$580
   4. D$1,160

   Explain your thinking. What would have to change for a different choice to be right?
4. 8

   Back to the modelFor the U-shaped pool, why did we subtract instead of add? When do you add areas and when do you subtract?

Use the words

Fill each blank with a word from the bank.

• A shape made of two or more basic shapes combined is a ___.
• To break a composite figure into basic shapes is to ___ it.
• To find the total area of separate parts, I ___ their areas.
• To find the area of a shape with a piece removed, I ___ the missing part's area.

Explain the thinking

1. 9

   Find the mistakeAnother student made this exact mistake in this lesson. Explain why it is wrong, then write what they should have done.

   The mistake: A common mistake in Area of Composite Figures is adding every piece even when a piece has been cut out of the figure.
2. 10

   Say moreFor the U-shaped pool you subtracted a 6 ft by 4 ft cutout from a 14 ft by 10 ft rectangle. How do you decide when to ADD areas and when to SUBTRACT?
3. 11

   Write your ownWrite your own problem about this situation, then solve it and show the answer. The situation: This is an L-shaped room from a floor plan. A dashed line splits it into two rectangles, and each part is labeled with its length and width.

   Show your work

Last check

These two come from Lesson 5.3. If they are shaky, that is the lesson to revisit — not this one.

1. 12

   Show what you knowExplain your thinking — A composite figure is made of a 9 ft x 7 ft rectangle and a 3 ft x 4 ft rectangle joined together. What is the total area?

   1. A12 sq ft
   2. B63 sq ft
   3. C75 sq ft
   4. D75 ft

   Explain your choice.
2. 13

   From Lesson 5.3Explain your thinking — A trapezoid has bases of 9 inches and 5 inches, and a height of 6 inches. What is its area?

   1. A27 sq in
   2. B42 sq in
   3. C42 in
   4. D84 sq in

   How do you know?
3. 14

   From Lesson 5.3Why add the two parallel edges and then take half?

   1. ABecause trapezoids are half of rectangles
   2. BBecause the average of the two bases acts like one rectangle's width
   3. CBecause 20 + 12 = 32 is easier
   4. DBecause the height must be halved

   How do you know?

Be honest — this tells your teacher what to do next