1. The total surface area of a cube of edge a is given by which formula?
- A6a²
- B4a²
- Ca³
- D6a
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Answer: A) 6a²
A cube has 6 equal square faces, each of area a². Total surface area = 6a².
Class 8 Surface Area of Cuboid and Cube — practice questions with answers
Mensuration · 5 sample questions from the school syllabus. Try each one, then open the answer and the worked solution.
2. The area of the four walls of a room 5 m x 4 m x 3 m (lateral surface area) is:
- A54 sq m
- B60 sq m
- C47 sq m
- D94 sq m
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Answer: A) 54 sq m
LSA = 2h(l + b) = 2 x 3 x (5 + 4) = 6 x 9 = 54 sq m.
3. A cube of edge 10 cm is painted on all faces. The total painted area is:
- A1200
- B600
- C660
- D540
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Answer: B) 600
TSA = 6a² = 6 x 100 = 600 sq cm.
4. A hall is 20 m long and 15 m wide. The cost of papering the four walls at Rs 12 per sq m is Rs 5040.
Find the height of the hall (in m).
Find the height of the hall (in m).
- A6
- B5
- C12
- D7
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Answer: A) 6
Wall area = = 420 sq m. LSA = 2h(l+b) = 2h(20+15) = 70h = 420, so h = 6 m.
5. A large cube of edge 6 cm is painted red on all faces, then cut into small cubes of edge 2 cm.
How many of the small cubes will have exactly one face painted red?
How many of the small cubes will have exactly one face painted red?
- A6
- B8
- C12
- D1
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Answer: A) 6
= 3 cubes per edge, so 27 small cubes. Cubes with exactly one painted face are the centre of each face: 1 per face x 6 faces = 6.
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