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①100-98+96-94+92-90+…+8-6+4-2,=(100-98)+(96-94)+(92-90)

来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/05/25 08:21:23
①100-98+96-94+92-90+…+8-6+4-2,
=(100-98)+(96-94)+(92-90)+…+(8-6)+(4-2),
=2+2+2+…+2+2,
=2×25,
=50;

②(25+125)×8,
=25×8+125×8,
=25×4×2+1000,
=200+1000,
=1200;

③(98+98+98+98)×25,
=98×4×25,
=98×(4×25),
=98×100,
=9800;

④785-(217+185),
=785-217-185,
=785-185-217,
=600-217,
=383;

⑤454+999×999+545,
=(454+545)+999×(1000-1),
=1000+999×1000-999,
=1000×(1+999)-999,
=1000000-999,
=999001;

⑥426+1999,
=426+(2000-1)
=426-1+2000,
=425+2000,
=2425.