Question

A triangular advertising board is 13 dm, 14 dm and 15 dm in length. Find the cost of painting it at ₹ 10 per dm².

Answer 1

Given:

• Sides of the triangular advertising board = 13 dm, 14 dm and 15 dm
• Cost of painting = ₹ 10 per dm²

Step-wise calculation:

1. Calculate the semi-perimeter (s) of the triangle: 

`S = (13 + 14 + 15)/2`

= `42/2`

= 21 dm

2. Calculate the area (A) of the triangle using Heron’s formula: 

`A = sqrt(s(s - a)(s - b)(s - c))`

= `sqrt(21(21 - 13)(21 - 14)(21 - 15))`

= `sqrt(21 xx 8 xx 7 xx 6)`

= `sqrt(7056)`

= 84 dm²

3. Calculate the cost of painting:

Cost = Area × Cost per dm²

= 84 × 10

= ₹ 840

The cost of painting the triangular advertising board is ₹ 840.