5分之3-5分之2x(5分之4-20分之1)
=3/5-2/5*(4/5-1/20)
=3/5-2/5*(16/20-1/20)
=3/5-2/5*17/20
=3/5-17/50
=30/50-17/50
=13/50
18x(3分之2+9分之4-6分之5)
=18×2/3+18×4/9-18×5/6
=12+8-15
=5
4分之1除于3分之2+2分之1x5分之4
=1/4×3/2+1/2×4/5
=3/8+2/5
=15/40+16/40
=31/40
2分之5加上2分之5乘5分之3加上5分2
=5/2+5/2×3/5+2/5
=5/2+3/2+2/5
=4+2/5
=4又5分之2