100*98分之97
=(98+2)*97/98
=98*97/98+2*97/98
=97+97/49
=97+1+48/49
=98又49分之48
99*98分之97
= （98+1）*97/98
= 98*97/98+1*97/98
=97+97/98
=97又98分之97