Question

A black board of sides 5m 20 cm and 3m 40 cm is to be painted. Find the cost of painting it at the rate Rs 12/m².

Answer 1

Given :

• Dimensions of a black board :-

• Length of the black board = 5 m 20 cm
• Breadth of the black board = 3 m 40 cm

To find :

• Cost of painting the black board

Solution :

Firstly, we will convert the length and breadth of the black board from 5 m 20 cm, 3 m 40 cm into m.

As we know,

1 cm = 1/100 m

20 cm = 20/100 = 2/10 = 0.2 m

Length of the black board = 5 + 0.2 = 5.2 m

• Length of the black board = 5.2 m

40 cm = 40/100 = 4/10 = 0.4 m

Breadth of the black board = 3 + 0.4 = 3.4 m

• Breadth of the black board = 3.4 m

Now, we will find the area of the black board.

Using formula,

Area = l × b

where,

• l = length of the black board
• b = breadth of the black board

Substitute the given values,

⇒ Area = 5.2 × 3.4

⇒ Area = 17.68

Area of the black board = 17.68 m²

Cost of painting 1 m² of black board = Rs. 12

Cost of painting 17.68 m² of black board = Rate × Area

⇒ 12 × 17.68

⇒ 212.16

Cost of painting the black board = Rs. 212.16