早教吧 育儿知识 作业答案 考试题库 百科 知识分享

计算:(1)299.9×19.98-199.8×29.97;(2)3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7;(3)27.8×28.7-27.7×28.8;(4)24.25×7.19+0.23×281+1.25×0.81;(5)0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99

题目详情
计算:
(1)299.9×19.98-199.8×29.97;
(2)3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7;
(3)27.8×28.7-27.7×28.8;
(4)24.25×7.19+0.23×281+1.25×0.81;
(5)0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99;
(6)999999×222222+333333×333334;
(7)1981×198319831983-1982×198119811981.
▼优质解答
答案和解析
(1)299.9×19.98-199.8×29.97
=29.99×199.8-199.8×29.97
=(29.99-29.97)×199.8
=0.02×(200-0.2)
=0.02×200-0.02×0.2
=4-0.004
=3.996;

(2)3.14+64.8×0.537×25+5.37×6.48×75-8×64.8×0.125×53.7
=3.14+6.48×5.37×25+5.37×6.48×75-8×12.5×5.37×6.48
=3.14+(25+75)×6.48×5.37-100×6.48×5.37
=3.14+100×6.48×5.37-100×6.48×5.37
=3.14+(100-100)×6.48×5.37
=3.14+0×6.48×5.37
=3.14+0
=3.14;

(3)27.8×28.7-27.7×28.8
=27.8×(28.8-0.1)-(27.8-0.1)×28.8
=27.8×28.8-27.8×0.1-27.8×28.8+28.8×0.1
=(27.8×28.8-27.8×28.8)-2.78+2.88
=0+2.88-2.78
=0.1;

(4)24.25×7.19+0.23×281+1.25×0.81
=(23+1.25)×7.19+23×2.81+1.25×0.81
=23×7.19+1.25×7.19×23×2.81+1.25×0.81
=(7.19+2.81)×23+(7.19+0.81)×1.25
=10×23+8×1.25
=230+10
=240;

(5)0.1+0.3+0.5+0.7+0.9+0.11+0.13+0.15+0.17+0.19+0.21+…+0.99
=(0.1+0.9)×5÷2+(0.11+0.99)×45÷2
=2.5+24.75
=27.25

(6)999999×222222+333333×333334
=333333×(3×222222)+333333×333334
=333333×666666+333333×333334
=(666666+333334)×333333
=1000000×333333
=333333000000;

(7)1981×198319831983-1982×198119811981
=1981×1983×1000100010001-1982×1981×1000100010001
=(1983-1982)×1981×1000100010001
=198119811981.