A wire of length 1 m and radius 0.1 mm has a resistance of 100 Q

A wire of length 1 m and radius 0.1 mm has a resistance of 100 Ω. Find the resistivity of the material.

Given l = 1m, r = 0.01 mm, R = 100 Ω
To find the resistivity §,
We know that R = pl/ A
p = R x A / L
= 100 x 0.22 / 7 / 1000
= 0.22 / 7 x 10 = 0.22 / 70 = 0.022 / 7 = 0.0031429 Ω-m
Area of the cross-section of the wire = $\pi$ ${{r}^{2}}$
= 22/7 x x 0.1 x 0.1 = 22.7 x 0.01 = 0.22 / 7
l = 1m = 1000mm