Question:
A closed iron tank 12 m long, 9 m wide and 4 m deep is to be made. Determine the cost of iron sheet used at the rate of Rs 5 per meter sheet, a sheet being 2 m wide.
Solution:
Length (l) = 12 m
Breadth (b) = 9 m
Height (h) = 4 m
Total surface area of the tank = 2[lb + bh + hl]
= 2[12*9 + 9*4 + 12*4]
= 2[108 + 36 + 48]
$=384 \mathrm{~m}^{2}$
The Length of the Iron sheet $=\frac{\text { Area of the Iron Sheet }}{\text { Width of the Iron Sheet }}$
= 384/2
= 192 m.
Cost of the Iron Sheet = Length of the Iron Sheet * Cost rate
= 192 * 5
= Rs. 960