Nylon-6,6 is made by step-growth polymerisation of hexane-1,6-diamine and hexanedioic acid, except that the diamine is used in a 2.0% molar excess…

With $r=1/1.02=0.98039$ and $p=0.99$, $\overline{X}_n=\dfrac{1+r}{1+r-2rp}=\dfrac{1.98039}{1.98039-1.94118}=50.5$ monomer residues per chain. Each residue (diamine or diacid) averages half of the repeating-unit mass, i.e. $226.3/2=113.2\ \mathrm{g\,mol^{-1}}$. Therefore $\overline{M}_n=50.5\times113.2\approx5.7\times10^3\ \mathrm{g\,mol^{-1}}$. If the feed were perfectly stoichiometric ($r=1$) the equation reduces to $\overline{X}_n=1/(1-p)=100$ and $\overline{M}_n\approx1.1\times10^4$, which is the trap. The slight excess of one monomer limits the chain length, because eventually both chain ends carry the same excess functional group and cannot react further. Hence the stoichiometric imbalance, not just the conversion, controls the degree of polymerisation, and the answer corresponds to chains of roughly fifty residues, i.e. about twenty-five repeating units each.