Answer
see solution
Work Step by Step
Let there are two wires of cross-section $A/2$, we can join them to form a wire of cross-section A.
Suppose, current I passes through each of the two small wires, and the potential difference between their ends is$ V$.
So the resistance of both wires will be $r = V/I$
Now when they are connected in parallel,
Current flowing through the wire= $2I,$
the potential difference between them =$ V$
So resistance of the bigger wire$ = V/2I = R = r/2$
Hence resistance is inversely proportional to the area of cross-section of the wire
