Two wires of same length and material have radii r and 2 r. The ratio of their specific resistance is what?

the resistance of a piece of wire is given as

R = ρl/A

so, the specific resistance will be

ρ = AR/l

or

ρ = πr²R/l

now, for the first wire

ρ = πr²R/l

for the second wire

ρ' = π(2r)²R/l

or

ρ' = π4r²R/l

so, the ratio will be

ρ/ρ' = [π(2r)²R/l] / [π4r²R/l]

thus,

ρ/ρ' = 1/4