、（81+7分之3）乘9分之7
=81x7/9+3/7x7/9
=63+1/3
=63又1/3
2、4分之3乘7加26分之21乘21分之13
=21/4+13/26
=21/4+2/4
=23/4
3、2减9分之7加2乘9分之7
=2-7/9+14/9
=2+7/9
=25/9