Q1. A plastic box 1.5m long, 1.25 m wide and 65 cm deep, is to be made.It is to be open at the top. Ignoring the thickness of the plastic sheet, determine:
S URFACE A REAS AND V OLUMES EXERCISE 13.1 Q1. A plastic box 1.5m long, 1.25 m wide and 65 cm deep, is to be made. It is to be open at the top. Ignoring the thickness of the plastic sheet, determine: (i). The area of the sheet required for making the box. (ii). The cost of sheet for it, if a sheet measuring 1m 2 cost Rs 20. Solution:- (i). (Given): l = 1.5 m, b = 1.25 m, h = 65 cm = 0.65 m Method-1: Surface Area of Cuboid = 2(lb + bh + hl) ∵ Box is to be open at the top ∴ Required Area of plastic sheet = (Surface Area of the Box) - (Area of top) = 2(lb + bh + hl) - (l x b) [or 2(bh + hl) + lb] = 2(1.5 x 1.25 + 1.25 x 0.65 + 0.65 x 1.5) - (1.5 x 1.25) = 2(1.875 + 0.8125 + 0.975) - (1.875) = 2(3.6625)