1999*9999\1998=1999*(1998*5+9)\1998=1999*5+1999*5\1998=9995+17991\1998
9999*1999/1998=9999*(1998+1)/1998=9999+9999/1998=9999+(9990+9)/1998 =9999+5+9/1998=10004+1/222
10004.0045045045045045045045045......