Question

plz answer question no. 13

Answer 1

Given external dimensions of the wooden bookshelf are:
Height = 110 cm, depth = 25 cm and breadth = 85 cm
Total surface area (external) of the shelf = 2(lb + bh + hl) sq units
= 2[110(85) + 85(25) + 25(110)]
= 2[9350 + 2125 + 2750]
= 2[14225] = 28450 sq cm
Cost of polishing external faces = Rs 0.20 × 28450 = Rs 5690
Given thickness of plank, w = 5 cm
Inner length = l – 2w =110 – 10 = 100 cm
Inner breadth = b – 2w = 85 – 10 = 75 cm
Inner depth = h – 2w = 25 – 10 = 15 cm
Total surface area of inner surfaces = 2[100(75) + 75(15) + 15(100)]
= 2[7500 + 1125 + 1500] = 2[10125] = 20250 sq cm
Cost of painting inner faces = Rs 0.10 × 20250 = Rs 2025

:) Hope this helps !!!

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