1)28.4*187-15.4*284+3.3*1.6=284*18.7-15.4*284+3.3*1.6=284*(18.7-15.4)+3.3*1.6=284*3.3+3.3*1.6=3.3*(284+1.6)=3.3*285.6=942.48
2)3.998/1.4*5.6/19.99=3.998÷19.99×(5.6÷1.4)=0.2×4=0.8
3)规律应该是:-3,-6,-12,-24,-48,-96,最后-99
所以1+2+3+……+99=4950
-3-6-12-24-48-96-99=-288
则答案为4950-288*2=4373(先消掉3,6,9……再减去3,6,9……)
4)(199.9+19.99+1.999+0.1999)/0.1111=(200-0.1+20-0.01+2-0.001+0.2-0.0001)/0.1111=(222.2-0.1111)/0.1111=222.2/0.1111-0.1111/0.1111=2222000/1111-1=2000-1=1999