A prismatic beam of trapezoidal section shown in figure is subjected to sagging B.M Calculate the ratio of b to b for maximum economy if the allowable stresses in tension and compression are 40 N/mm and 50 N/mm respectively. Kb 3 N/W T d (a) (c) 2/1/2 2 N b n A Id-n (b) 2/3 (d) 2