A metal rod A of length ℓ0 expands by Δℓ when its temperature is raised by 100oC. Another rod B of different metal of length 2ℓ0 expands by Δℓ/2 for same rise in temperature. A third rod C of length 3ℓ0 is made up of pieces of rods A and B placed end to end expands by 2Δℓ on heating through 100K.The length of each portion of the composite rod is: