The bases of trapezoid $ABCD$ are $\overline{AB}$ and $\overline{CD}$. Let $M$ be the midpoint of $\overline{AD}$. If the areas of triangles $ABM$ and $CDM$ are 5 and 17, respectively, then find the area of trapezoid $ABCD$.
since M is the midpoint of AD, the altitude to M is half the altitude of ABCD. The triangles have the same bases as ABCD, so the sum of the two triangles is half the area of the trapezoid.
15 is not the answer
It is 44
The answer is always 21.
Or maybe it's 22. Oh well, guess it's too late now anyway.