The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x, respectively are T2 and T1 (T2 > T1). The rate of heat transfer through the slab, in a steady state is \[\left( \frac{A({{T}_{2}}-{{T}_{1}})K}{x} \right)f\], with ¦ which equal to [AIEEE 2004]

• A.            1
• B.            \[\frac{1}{2}\]
• C.            \[\frac{2}{3}\]
• D.            \[\frac{1}{3}\]