С23=С2*С3/(С2+С3)=2С*С/3С=С*2/3
с45=С4*С5/(С4+С5)=2С*С/2*(2С+С/2)=С*2/5
с456=с45*С6/(с45+С6)=2*С*3С/5*((С*2/5)+3С)=С*6/17
с23456=с23+с456=С((2/3)+6/17)=С*52/51
с123456=С*52/51*С/((С*52/51)+С)=С*52/103
Сob=с123456*C7/(с123456+C7)=(С*52/103)*C*3/((С*52/103)+C*3)=C*156/361