五分之二加十分之九乘以六分之五.（四分之三减五分之二）乘以二十.八分之七比四分之

2/5+9/10x5/6 (3/4-2/5)x20 7/8-3/4x5/18 (10-3/8)x12/11
=2/5x3/2 =3/4x20-2/5x20 =7/8-5/24 =10x12/11-3/8x12/11
=3/5 =10-8 =2/3 = 120/11-9/22
=2 =231/22