Hence, if diameter doubles, resistance becomes 1/4 times.

What happens to the resistance when diameter is doubled?

From this relation we can conclude that resistance is inversely proportional to area A of the conductor. Area of the conductor becomes 4 times the area of the conductor without doubling the diameter. Thus, we can say that new resistance will decrease four times.

What will be the resistance if radius is doubled?

When radius is doubled, Resistance decreased 2² times which is 4.