Question

The edges of a triangular board are $6cm,8cm$ and $10cm$. The cost of painting it at the rate of $9$ paise per $c{m}^2$ is

• A. Rs. $2.00$
• B. Rs. $2.16$
• C. Rs. $2.48$
• D. Rs. $3.00$

Answer 1

Answer: (B)

Rs. $2.16$

$s=\frac{a+b+c}{2}=\frac{6+8+10}{2}=12$

By Heron's formula,
Area of the triangle $=\sqrt{s(s-a)(s-b)(s-c)}=\sqrt{12(12-6)(12-8)(12-10)}$
$=\sqrt{12\left(6\right)\left(4\right)\left(2\right)}=24c{m}^2$
Cost of painting $=9\times 24$ paise $=216$ paise $=$ Rs. $2.16.$