Dear candidates,

Givern

Three Rods having same length and same area

K = 1 , K = 2 , K = 3

we have

Reff = R1 + R2 + R3

R = L/KA

3L/A*Keff = L/1*A + L/2*A + L/3*A

so L/ A will  be cancel

we get

3/keff = 1 + 1/2 + 1/3

3/keff = 6+ 3 + 2 /  6

3/keff = 11/6

keff = 18/11 = 1.6

Hope this helps!!

All the Best!!