Two equal resistances, 400 $$\Omega$$ each, are connected in series with a 8 V battery. If the resistance of first one increases by 0.5%, the change required in the resistance of the second one in order to keep the potential difference across it unaltered is to

The effective resistance between A and B in the figure is $${7 \over {12}}\Omega $$ if each side of the cube has 1$$\Omega$$ resistance. The effective resistance between the same two points, when the link AB is removed, is