Explanation:
2.
if parallel, the ratio of the line segments AD/DB must be the same as AE/AC.
4/2 = 2
but
9/5 is not 2 (10/5 would be 2).
so, they are not parallel.
3.
the area of a right-angled triangle is half the area of a rectangle with the same side lengths.
so, the area of ABC is
4×5/2 = 20/2 = 10
since D and E are midpoints, they are splitting the sides in half.
so, AD is only half as long as AC. the same for CE and CB.
so, the area of DEC is
2×2.5/2 = 5/2 = 2.5
the scale factor of the sides does apply to the area in a way, but not 1:1.
as the area is calculated by multiplying 2 sides, the scale factor is entering the calculation for each side and therefore twice. that means the scale factor is multiplied by itself.
so, the scale factor of the areas is in fact the square of the scale factor of the side lengths.
therefore, in our example here, the scale factor of the side lengths is 1/2. and the scale factor of the areas is (1/2)² = 1/4.
and indeed, 10× 1/4 = 10/4 = 2.5