能简算的要简算 列式计算

4/5÷[5/8×（1-1/5）]
=4/5÷【5/8 ×4/5】
=4/5÷1/2
=8/5
86×4/85 =
=（85+1）×4/85
=4+4/85
=4又4/85

9/17×1/7+5/17÷7
=9/17×1/7 +5/17×1/7
=（9/17 + 5/17）×1/7
=14/17×1/7
=2/17
2/5÷(3/4+2/5)
=2/5÷23/20
=2/5×20/23
=8/23