If the height of a triangle is decreased by 40% and it’s base is increased by 40% , what will be the effect on its area?

Let base and height of the triangle be 10 cm each

Area of original triangle, $$\triangle = \frac{1}{2} \times 10 \times 10 = 50$$ $$cm^2$$

If the height of a triangle is decreased by 40%, => New height = $$10-\frac{40}{100} \times 10=6$$ cm

and it’s base is increased by 40%, => New base = $$10+\frac{40}{100} \times 10=14$$ cm

Area of new triangle, $$\triangle' = \frac{1}{2} \times 6 \times 14 = 42$$ $$cm^2$$

$$\therefore$$ Area decreases by = $$\frac{\triangle - \triangle'}{\triangle} \times 100$$

= $$\frac{50-42}{50} \times 100 = 8 \times 2=16\%$$

=> Ans - (D)