1That's easy......The three numbers are in G.P....This is how
Let the three numbers be x,y,z
Now x,y,z are in A.P.
Therefore 2y=x+z..........(1)
Also x,y,z are in H.P
therefore 1x, 1y, 1z are in A.P
i.e 2y=1x+1z
=x+zxz
=2yxz (from 1)
Therefore y2 =xz
Thus x,y,z are in G.P