5/17×1/7×51
=5/17x51x1/7
=15x1/7
=15/7
3/4×125+3/4×25
=3/4x(125+25)
=3/4x150
=450/4
3/4÷（3/4+2/5）
=3/4÷23/20
=15/23
4/3÷3/4×3/4
=4/3x3/4÷3/4
=1÷3/4
=4/3
如果本题有什么不明白可以追问,