Estimate the quantity of plastering required to plaster both the face of a wall of 5 m long, 4 m high and 30 cm thickness. Ignore thickness faces of wall.
- A20 m²
- B50 m²
- C40 m²Correct
- D24 m²
Solution
Concept
Plastering is measured in square metres as length × height for each face plastered.
Formula
Area = n × L × H
Step-by-step solution
1. Length L = 5 m, height H = 4 m. 2. Area of one face = 5 × 4 = 20 m². 3. Both faces are plastered, so n = 2. 4. Total area = 2 × 20 = 40 m². 5. Thickness faces are ignored, so the 30 cm thickness is not used. 6. Answer: 40 sq m, option C.
Explanation
Plaster area is length × height for one face. The question asks for both faces, so we double it. The wall thickness is not needed because the edge faces are ignored.
Why the other options are wrong
A: 20 sq m is for one face only. B: 50 sq m does not match any correct calculation. D: 24 sq m wrongly mixes in the thickness or adds wrong values.
Shortcut
2 × L × H = 2 × 5 × 4 = 40 sq m.
Common mistake
Calculating only one face, or using the thickness (volume) for plastering, which is an area item.
Correct answer: C) 40 m²