**Question:**

A tank open at the top is made of iron sheet 4 m wide. If the dimensions of the tank are 12 m × 8 m × 6 m, find the cost of iron sheet at Rs 17.50 per metre.

**Solution:**

An open iron tank of dimensions $12 \mathrm{~m} \times 8 \mathrm{~m} \times 6 \mathrm{~m}$ is to be made.

Surface area of the open tank $=$ (area of the base) $+$ (total area of the 4 walls)

$=(12 \times 8)+2 \times(8 \times 6+12 \times 6)$

$=(96)+2 \times(48+72)$

$=336 \mathrm{~m}^{2}$

Also, it is given that the cost of the iron sheet that is $4 \mathrm{~m}$ wide is Rs $17.50$ per metre.

i.e., the area of the iron sheet $=1 \mathrm{~m} \times 4 \mathrm{~m}=4 \mathrm{~m}^{2}$

So, the cost of $4 \mathrm{~m}^{2}$ of iron sheet $=$ Rs $17.50$

$\therefore$ The cost of iron sheet required to an iron tank of surface area $336 \mathrm{~m}^{2}=336 \times \frac{17.50}{4}=$ Rs 1470