Question

The base of a triangle is $15cm$ and height is $12cm$. The height of another triangle of double the area having the base $20cm$ is:

• A. $8cm$
• B. $9cm$
• C. $12.5cm$
• D. $18cm$

Answer 1

The correct option is D $18cm$

Area of first triangle, $A_1=\frac{1}{2}\times base\times height=\frac{1}{2}\times 15\times 12=90c{m}^2$
area of second triangle, $A_2=2A_1$
$\frac{1}{2}\times base\times height=2\times 90$
$\frac{1}{2}\times 20\times height=180$
height$=\frac{180\times 2}{20}=18cm$