Three rods of identical cross-section and lengths are made of three different materials of thermal conductivity K1,K2 and  K3 respectively.  They are joined together at their ends to make a long rod (see figure).  One end of the long rod is maintained at 100°C and the other at 0°C (see figure).  If the joints of the rod are at 70°C and 20°C in steady state and there is no loss of energy from the surface of the rod, the correct relationship between  K1,K2 and K3