Center of mass of a system of particles is given by the formula.

$\frac{{\mathrm{m}}_1{\mathrm{x}}_1+{\mathrm{m}}_2{\mathrm{x}}_2+{\mathrm{m}}_3{\mathrm{x}}_3+.....}{{\mathrm{m}}_1+{\mathrm{m}}_2+{\mathrm{m}}_3+....}$

where m₁, m₂ ... are their masses and x₁, x_2,... are their x coordinates

then if 1kg, 2kg, 3kg, ..........49kg are at 1cm, 2cm, 3cm, ....49 cm their center of mass is at