Question

30. Rahul wants to paint all the four square walls of his room of side 10 m. If the cost of
Painting is Rs. 20 per sq. m then what will be the total cost of painting?
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Answer 1

$\huge\star{\green{\underline{\mathfrak{Answer :-}}}}$

GIVEN :-

Four square walls of 10 m side.

Rate of painting is rupees 20 per square metre.

TO FIND :-

Cost of painting

SOLUTION :-

Total surface area of 4 walls = $\tt 4 \times {l}^{2}$.

So, Area = $\tt 4 \times {10}^{2}$

= $\tt 400 {m}^{2}$

The cost = 20 × 400

= Rupees 8000

___________

Formulas related to square and cube :-

• Total surface area of cube is $\tt 6 \times {l}^{2}$.

• Lateral surface area of cube is $\tt 4 \times {l}^{2}$.

• Volume of cube is $\tt {l}^{3}$.

• Perimeter of square is $\tt 4 \times l$.

• Area of a square is $\tt {l}^{2}$.

___________

Answer 2

Given,

The length of the square walls is 10m

• $\sf{A = 10m}$
• Cost of painting one square metre is 20 rupees

Now,

The four square walls would form a cube

And since only the four walls are to be painted,we find the Lateral Surface Area of the Cube

To finD

LSA of Cube

$\boxed{\mathtt{LSA = 4{A}^{2}}}$

$\sf{\longrightarrow 4 \times {10}^{2} } \\ \\ \longrightarrow 4 \times 100 \\ \\ \sf{ \longrightarrow \: 400 \: {m}^{2} }$

• Painting one square metre costs 20 rupees

• Painting 400 m² would cost : 400 × 20 = 8000 rupees

The total cost of painting is 8000 rupees