# The edges of a triangular board are 6 cm, 8 cm and 10 cm. The cost of painting it at the rate of 9 paise per cm² is

a. Rs 2.00

b. Rs 2.16

c. Rs 2.48

d. Rs 3.00

**Solution:**

Given, the edges of a triangular board are 6 cm, 8 cm and 10 cm.

We have to find the cost of painting it at the rate of 9 paise per cm²

Given, a = 6 cm

b = 8 cm

c = 10 cm

By __Heron’s formula__,

Area of triangle = √s(s - a)(s - b)(s - c)

Where s= semiperimeter

s = (a + b + c)/2

Now, s = (6 + 8 + 10)/2

= 24/2

s = 12 cm

Area of triangle = √[12(12 - 6)(12 - 8)(12 - 10)]

= √[12(6)(4)(2)]

= √[12(24)(2)]

= √[12 × 12 × 2 × 2]

= 12 × 2

Area = 24 cm²

The cost of painting area of 1 cm² = 9 paise

Cost of painting entire area = 24 × 9

= 216 paise

= 216/100

= Rs. 2.16/-

Therefore, the cost of painting the triangular board is Rs. 2.16/-

**✦ Try This: **The edges of a triangular board are 7 cm, 8 cm and 9 cm. The cost of painting it at the rate of Rs. 1.50 per cm² is

**☛ Also Check: **NCERT Solutions for Class 9 Maths Chapter 12

**NCERT Exemplar Class 9 Maths Exercise 12.1 Problem 9**

## The edges of a triangular board are 6 cm, 8 cm and 10 cm. The cost of painting it at the rate of 9 paise per cm² is a. Rs 2.00, b. Rs 2.16, c. Rs 2.48, d. Rs 3.00

**Summary:**

The edges of a triangular board are 6 cm, 8 cm and 10 cm. The cost of painting it at the rate of 9 paise per cm² is Rs. 2.16/-

**☛ Related Questions:**

- If a, b, c are the lengths of three sides of a triangle, then area of a triangle = √s(s - a)(s - b)( . . . .
- The area of a triangle with base 4 cm and height 6 cm is 24 cm². Is the given statement true or fals . . . .
- The area of ∆ ABC is 8 cm² in which AB = AC = 4 cm and ∠A = 90º. Is the given statement true or fals . . . .

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