A uniform wire of resistance 36 ohm is bent in the form of a circle as shown in fig  The effective resistance across the points A and B is

Let r be the resistance of total length of circular wire' The resistance of smaller arc AB,r1=r/6=36/6=6Ω The resistance of bigger arcr2=5r/6=(5×36)/6=30Ω Resistances r1 and r2 are in parallel between points A and B, Therefore,1R=1r1+1r2=16+130=630=15∴R=5Ω