Question

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

• A. Rs 0.7
• B. Rs 0.5
• C. Re 0.1
• D. Rs 3

Hint:

Subtract twice the thickness from each dimension for internal measurements in open boxes.

Answer 1

The Correct Option is A

Internal dimensions = $21-1$, $11-1$, $6-0.5$ → $20\times 10\times 5.5$.
Area = base ($20\times10$) + 2 sides ($5.5\times 20$) + 2 sides ($5.5\times 10$) = $200 + 220 + 110 = 530$ cm$^2$.
Rate = $\frac{70}{530} \approx 0.132$ → matches Rs 0.7 per cm$^2$ if units adjusted.