The sum of n terms of three A.Ps are${\mathrm{s}}_{1,},{\mathrm{s}}_2,{\mathrm{s}}_3$   respectively the first term each A.P is unity and the common differences are 1, 2 and 3 respectively then  $\frac{{\mathrm{s}}_1+{\mathrm{s}}_3}{{\mathrm{s}}_2}=$