Cramer's rule, Quarks Fractional electric charge, A scientific exploration or a possible mathematical electric charge value?

In linear algebra, [Cramer's rule][1] is an explicit formula for the solution of a system of linear equations with as many equations as unknowns. 2u+1d=1 1u+2d=0 $a_1d+b_1u=c_1$, $a_2d+b_2u=c_2$ $u=\frac {c_1b_2-c_2b_1}{a_1b_2-a_2b_1}$ and $d=\frac {a_1c_2-a_2c_1}{a_1b_2-a_2b_1}$ u=+2/3 d=-1/3 now i think an up quark has no electric charge and infact this is down quark which has electeric charge of (+1,-1), then fractional electric charge completely breakdown 2u(0)+1d(+1)=+1 1u(0)+d(-1)+d(+1)=0 which means probabilities is associated with unknown parameters, Thus, Quarks fractional electric charge value is possible charge of quarks ``not'' accurate value. And also it is consisted with neutron decay, While bound neutrons in stable nuclei are stable, free neutrons are unstable; they undergo beta decay with a mean lifetime of just under 15 minutes (881.5 $\pm$ 1.5 s). (thanks god!) Free neutrons decay by emission of an electron and an electron antineutrino to become a proton, a process known as beta decay $n^0 \to p^{+1}+e^{-1}+\overline \nu_e$ \\[4pt] [1]: http://en.wikipedia.org/wiki/Cramer's\_rule