Find what length of canvas 2 m in width is required to make a conical tent 20 m in diameter and 42 m in slant height allowing 10% for folds and the stitching. Also find the cost of the canvas at the rate of ₹80 per meter.

Given diameter of conical tent = 20 m and l = 42 m.

Radius = $\dfrac{\text{Diameter}}{2} = \dfrac{20}{2}$ = 10 m.

We know that curved surface area of cone = π × radius × slant height.

Putting values we get,

Curved surface area of tent = $\dfrac{22}{7}$ x 10 x 42 = 22 × 10 × 6 = 1320 m².

10% of 1320 = $\dfrac{10}{100}$ x 1320 = 132 m².

Total area of canvas required for making tent = 1320 + 132 = 1452 m².

Area of rectangular cloth = l × b.

∴ l × b = 1452
⇒ l × 2 = 1452
⇒ l = $\dfrac{1452}{2} = 726$ m.

Since, the cost of canvas = ₹ 80/meter.

∴ The cost of 726 m of canvas = ₹ 726 × 80 = ₹ 58080.

Hence, the length of canvas required to make conical tent is 726 m and the cost of canvas = ₹ 58080.