题目是不是：计算下面各题1/3x3/5+1 5/7-5/9x5/7 1-5/7x21/25 1/2+5/4x4/5 1/6x(5-2/3) 7/8x7+3/8 =1/5+1 =5/7-25/63 =1-3/5 =1/2+1 =1/6x13/3 =49/8+3/8=6/5 =45/63-25/63 =2/5 =3/2 = 13/18 =13/2=20/63...