Perimeter, Area, and Surface Area — Answer Key
Part A: Fill in the Blank
Write the missing word or number on each line.
1. A triangle with base 8 cm and height 5 cm has area 20 sq cm.
A = 1/2 x 8 x 5 = 20 square centimeters using the triangle area formula.
2. An L-shape made of a 6x4 and a 3x2 rectangle has area 30 sq ft.
6 x 4 = 24 and 3 x 2 = 6, so total area = 24 + 6 = 30 square feet.
3. A triangle with base 10 m and height 7 m has area 35 sq m.
A = 1/2 x 10 x 7 = 35 square meters by the triangle area rule.
4. A T-shape with a 8x3 top and 4x5 stem has total area 44 sq in.
8 x 3 = 24 and 4 x 5 = 20, so 24 + 20 = 44 square inches total.
5. Half of base 12 ft times height 6 ft for a triangle gives 36 sq ft.
1/2 x 12 x 6 = 36 square feet for the triangle area.
6. Two rectangles, 5x4 and 5x3, joined as an L have area 35 sq cm.
5 x 4 = 20 and 5 x 3 = 15, so combined area is 20 + 15 = 35 sq cm.
7. Triangle with base 9 in and height 4 in has area 18 sq in.
1/2 x 9 x 4 = 18 square inches using the triangle area formula.
8. An L-shape decomposes into a 7x6 and a 2x3 rectangle; total area is 48 sq m.
7 x 6 = 42 and 2 x 3 = 6, so total area = 42 + 6 = 48 square meters.
9. A right triangle has legs 6 cm and 8 cm; its area is 24 sq cm.
A = 1/2 x 6 x 8 = 24 square centimeters since the legs are perpendicular.
Part B: Matching
Match each item on the left to the correct answer on the right.
1. Match each item to its correct answer.
Rectangle area
→ Decompose into rectangles, then add
Decompose into rectangles, then add
Triangle area
→ A = 1/2 x base x height
A = 1/2 x base x height
Square perimeter
→ A = length x width
A = length x width
L-shape area
→ P = 4 x side
P = 4 x side
Rectangle area is l x w, triangle area is half base times height, square perimeter is 4 times a side, and L-shapes need decomposition.