Question

box is made up of wood 3 cm thick its external Length breadth and height are 1.48 m 1.16 m and 8.3 dm respectively find the cost of painting the inner surface at rupees 50 per square metre

Answer 1

External Length = 1.46 m
Inner Length = 1.46 m - (0.3 m + 0.3 m)
= 1.40 m or 140 cm

External Breadth = 1.16 m
Inner Breadth = 1.16 m - (0.3 m + 0.3 m)
= 1.10 m or 110 cm

External Height = 8.3 dm or 83 cm
Inner Height = 83 cm - 3 cm = 80 cm

Cost of painting = 75 paise per 100 sq cm

Cost of painting the bottom from inside = 140*110*(75/100)
= 11550 paise or  Rs.115.50

Cost of painting the four sides = (2*140*80 + 2*80*110)*(75/100)
= (22400 + 17600)*(75/100)
= (40000*75)/100
= 30000 paise or Rs. 300

Total cost of painting from inside = Rs. 115.5 + Rs. 300 
= Rs. 415.50 
Answer.

Answer 2

i hope you understand this ..
Given thickness of wood = 3 cm 
Length of open box = 1.48 m = 148 cm
 Breadth of open box = 1.16 m = 116 cm 
Height of open box = 8.3 dm = 83 cm 
Inner length, l = outer length – twice width= 148 – 6 = 142 cm
 Outer breath = 116 – 6 = 110 cm 
Outer height = 83 – 3 = 80 cm [since it is an open box]
Area of inner surface = 2(lb + bh + hl) – lb= 2[142 x 110 + 110 x 80 + 80 x 142] – [142 x 110] = 55940 sq cm
 Cost of painting inner surface = Rs (50/100) x (55940/100) = Rs 279.90