Mathcad Professional 14.0alal2A203D355-B529-4315-939E-3F9C035FEE2771ECC66D-02D1-4394-9A25-51397217604600000000-0000-0000-0000-00000000000000000000-0000-0000-0000-000000000000
One task about an epidemicsee -
http://twtmas.mpei.ac.ru/mas/Worksheets/rkfixed_2ODE.mcd