Let $ABCD$ be a regular tetrahedron. Let $E$, $F$, $G,$ $H$ be the centers of faces $BCD$, $ACD$, $ABD$, $ABC$, respectively. The volume of pyramid $DEFG$ is $18.$ Find the volume of pyramid $EFGH$
The base of EFGH = the base of DEFG
The height of pyramid EFGH is (1/2) that of pyramid DEFG
So....the volume of pyramid EFGH = (1/2)(18) = 9
+1756 
