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Three metal rods A,B and C of same lengt...

Three metal rods A,B and C of same length and cross-section are placed end to end and a temperature difference is maintained between the free ends of A and C. If the thermal conductivity of `B(K_(B))` is twice that of `C(K_(C))` and half that of `A(K_(A))`, then the effective thermal conductivity of the system will be

A

`(K_(A))/7`

B

`(6K_(B))/7`

C

`(7K_(B))/3`

D

`7K_(c)`

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