The area of a triangle is constant. Find the percentage increase in its perpendicular height if the base of the triangle is decreased by 20%.

Correct option is D

Given:
Area of a triangle remains constant.
Base decreases by 20%.
Formula Used:
Area = $$\frac12$$​× Base × Height
If area is constant => Base × Height = Constant
Thus, Height ∝ 1/Base
Solution:
Let original base = B
Let original height = H
New base = 0.8B
Since area is constant:
B × H = 0.8B × H'
H = 0.8H'
H' =$$\frac{H}{0.8}$$​= 1.25H
Increase in height = 1.25H − H = 0.25H
Percentage increase = $$\frac{0.25H}{H}$$​× 100 = 25%