Three rods AB,BC and BD made of the same material and having the same cross- section have been joined as shown in the figure. The ends A,C and D are held at temperatures of $20^{\circ},80^{\circ}$ and $80^{\circ}$ respectively. If each rod is of smme length, then the temperature at the junction B of the three rods is :

Question

$(1) \;90^{\circ }$

$(2) \;60^{\circ }$

$(3) \;40^{\circ }$

$(1) \;30^{\circ }$