A plastic box 1.5 m 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 1 m2 costs Rs 20.
Here, l = 1.5 m, b = 1.25 m, h = 65 cm = 0.65 m.
Since the box is open at the top, it has only five faces.
(i) So, surface area of the box = lb + 2(bh + hl)
= 1.5 × 1.25 m2 + 2 (1.25 × 0.65 + 0.65 × 1.5) m2
= 1.875 + 2 (1.7875) m2
= (1.875 + 3.575) m2 = 5.45 m2
Hence, 5.45 m2 of sheet is required Ans.
(ii) Cost of 1 m2 of the sheet = Rs 20
∴ cost of 5.45 m2 of the sheet = Rs 20 × 5.45 m2 = Rs 109 Ans