1、158-92+42-8
=（158+42）-（92+8）
=200-100
=100
2、58/7-28.5+3.85
= -2291/140
3、3.5×1.25+1.25×2.7-3.8÷ 4/5
=3.5×1.25+1.25×2.7-3.8×1.25
=（3.5+2.7-3.8）×1.25
=2.4×1.25
=0.3×8×1.25
=3
4、6×1/4＋13÷4-18×0.25
=6×1/4＋13×1/4-18×1/4
=（6+13-18）×1/4
=1×1/4
=1/4