Adding & Subtracting Areas Flashcards

All 6 cards in this deck

What is a composite shape?

A shape made up of two or more basic shapes joined together.

What are the two ways of finding the area of an L-shaped shape?

Split it into rectangles and add the areas; or find the area of the surrounding rectangle and subtract the missing piece.

What are the steps to find the area of a composite shape by adding areas?

e.g. a shape split into a 5 cm by 2 cm rectangle and a 3 cm by 2 cm rectangle

1. Split the shape into basic shapes: two rectangles
2. Find each area: $10$ cm² and $6$ cm²
3. Add them: $16$ cm²

What are the steps to find a shaded area when a smaller shape is cut out of a larger one?

e.g. a 3 cm by 2 cm rectangle removed from a 10 cm by 6 cm rectangle

1. Area of the whole outer shape: $60$ cm²
2. Area of the piece removed: $6$ cm²
3. Subtract: shaded area $= 54$ cm²

True or false? When a shape is split into two parts, the area of the whole shape is the sum of the areas of the two parts.

True. Areas of the separate pieces add to give the total area.

True or false? If a semicircle sits on the 10 cm side of a rectangle, so that side is its diameter, its area is $\frac{1}{2}\pi \times 10^2$.

False. The radius is half the diameter, so the area is $\frac{1}{2}\pi \times 5^2$.