Problem: When the base of a triangle is increased 10% and the altitude to this base is decreased 10%, the change in area is:
Answer Choices:
A. 1% increase
B. 21% increase
C. 0%
D. 21% decrease
E. 1% decrease
Solution:
K0=21bh,Kn=21(b+.1b)(h−.1h)∴Kn=21bh+.05bh−.05bh−21(.01)bh=(1−.01)K0. Therefore, the change is a decrease of 1% of the original area.