Question

A wooden box (open at at top) of thickness 0.5 cm, lenght 21 cm, width 11 cm and height 6 cm is painted on the inside. The expenses of painting are 70 rupees. What is the rate of painting per square centimetre ?​

Answer 1

Answer:

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As the box has to be painted from inside, the internal dimensions are:

Length = (21 – 0.5 – 0.5) = 20 cm,

Breadth = (11 – 0.5 – 0.5) = 10 cm,

Height = (6 – 0.5) = 5.5 cm

Total area to painted

= Area of four walls + Area of base

= 2 × (10 × 5.5 + 20 × 5.5) + (20 × 10)

= 2 × (55 + 110) + 200 = 530 square centimetre.

Since the total expense of painting this area is

70 rupees, the rate of painting = 70/530 = 0.13 rupees

= 0.1 rupees approx.

Answer 2

Answer:

Rupees = 0.1 per cm3

Step-by-step explanation:

As the box is painted from inside, the dimensions of the box from inside are

Length = (21 - 05 - 05) = 20 cm

Breadth = (11 - 05 - 05) = 10 cm

Height = (6 - 05) = 5.5

Total number of faced to be painted = 4 walls + One base

The dimensions of two of the walls = 2 x (10 x 5.5)

The dimensions of the remaining two = 2 x (20 x 5.5) and

that of the base = (20 x 10 ) and

so the total area to be pained = 2 x (10 x 5.5) + 2 x (20 x 5.5) + (20 x 10)= 530cm3

Since, the total expenses of painting this area is ₹70, the rate of painting

= 70/530 = 0.13 = ₹ 0.1 per cm3 (approx)