Area of triangle formula : ½ × base × height


So A = ½ × b × h = ½bh



Height has increased by 10% so height is now 110% of the original h.

110% of h = 110/100 of h = 1.1 times of h

So the height now is 1.1h


Base has deceased by 20% so base is now 80% of the original b.

80% of b = 80/100 of b = 0.8 times of b

So the height now is 0.8b.



New area would be :


B = ½ × 0.8b × 1.1h

= 0.8 × 1.1 × ½bh

= 0.88 (½bh)

= 0.88 A

Or even more simply,


B = (0.8)(1.1)A = 0.88A



Or


B = 80/100 × 110/100 × A

= 4/5 × 11/10 × A

= 22/25 A