Question

A conductor of radius r, length and resistivity ρ has resistance r. what is the new resistance if it is stretched to 4 times its original length?'

Answer 1

The resistance of a conductor is given by
$R= \frac{\rho L}{A}$
where L is the length of the wire, $\rho$ the resistivity of the material and A the cross-sectional area.

We can see that if all the other quantities do not change, if the new length of the conductor is 4 times the original length: $L'=4 L$, then the new resistance is also 4 times the original value:
$R'= \frac{\rho L'}{A}= \frac{\rho 4 L}{A}=4 \frac{\rho L}{A}=4 R$