A closed iron tank 12m long, 9m wide and 4m deep is to be made. Determine the cost of iron sheet used at the rate of Rs. 5 per metre sheet, sheet being 2 metre wide.

Explanation

Total surface area of tank`=2(lb+bh+hl)`
`=2[12xx9+9xx4+12xx4]`
`=2[108+36+48]`
`=384m^2`
Now length of iron sheet`=(384)/("width of iron sheet" )`
`=384/2=194m.`
Cost of iron sheet = length of sheet x cost rate 
`=192xx5=Rs.960`