Question

An open box is made of wood 3 cm thick .Its external Length breadth and height are 1.48 m, 1.16 m and 8.3 dm . find the cost of painting the inner surface area of Rs.50 per square metre.

Answer 1

Given It is an open box
thickness of wood (t) = 3 cm
External Length of the box (L)= 1.48 m
External Breadth of the box (B)= 1.16 m
External Height of the box (H) = 8.3 dm

Inner length, l = External length – twice the thickness of the wood
=1.48 -2*(0.03) = 1.48-.06=1.42 m
Inner Breadth b= External Breadth - twice the thickness of the wood
= 1.16 -0.06 = 1.10 m
Inner Height h= External Height - thickness of the wood (since it is an open box)
=0.83-.03 = 0.8 m

Area of inner surface = 2(lb + bh + hl) – lb
= 2[1.42 x 1.10 + 1.10 x .80 + .80 x 1.42] – [1.42 x 1.10]
= 5.5940 sq meter

Cost of painting the inner surface area = cost of per square meter x area of inner surface
=50* 5.5940 = 279.90 Rupees