Look at the following triangle CDE. A is the midpoint
of DE, and CD = 3BC. The area of the shaded region is 6 cm^{2}.
What is the area of ∆CDE?

cm^{2}

Since ABC and ABD have the same height, but different
bases, the area of ABD is 3 times the area of ABC. Thus it has an area of 6 × 3
= 18. Since ACD and ACE have the same height and also the same bases, they have
the same area too. Thus DEC is 18 + 18 = 36 cm^{2}