:①(38.7-18.6÷3.1)×0.8 =26.16
②7.09×10.8-8×0.709=0.709×108-8×0.709=0.709×(108-8)=70.9
③15.6×13.1-15.6-15.6×2.1=15.6×(13.1-1-2.1)=156
④20÷1.25÷8=20÷(1.25×8)=2
:①(38.7-18.6÷3.1)×0.8 =26.16
②7.09×10.8-8×0.709=0.709×108-8×0.709=0.709×(108-8)=70.9
③15.6×13.1-15.6-15.6×2.1=15.6×(13.1-1-2.1)=156
④20÷1.25÷8=20÷(1.25×8)=2