13分之7×9分之5+13分之4×9分之7
=7/13*5/9+4/13*7/9
=5/13*7/9 +4/13*7/9
=7/9*(5/13+4/13)
=7/9*9/13
=7/13
97×98分之3
=(98-1)*3/98
=98*3/98-1*3/98
=3-3/98
=2又95/98
（12分之5＋5分之3）×12×5
=5/12*12*5+3/5*5*12
=5*5+3*12
=25+36
=61确保答案是对的吗？没问题