奥数四年级—简便运算(二).ppt

单击此处编辑母版标题样式,*,这节，我们主要介绍一些有一定难度的、用凑整和分解等方法进行的乘、除法的速算。,简便运算（二）,例,1,、,999,888,111,=9,111,8,111,111,=9,111,8,(111,111),=9,8,111,(111,111),=72,111,=7992,例,1,、,25,5,64,125,拆分,凑整,=25,5,(2,32),125,=25,5,(2,4,8),125,=(25,4),(5,2),(125,8),=100,10,1000,=1000000,75,16,=3,25,4,4,=(25,4),(4,3),=100,12,=1200,例,2125,(10+8),乘法分配律,=125,10,+,125,8,=1250+1000,=2250,(20-4),25,=20,25-4,25,=500-100,=400,4004,25,=(4000+4),25,=4000,25+4,25,=100 000+100,=100100,125,798,=125,(800-2),=125,800-125,2,=1000 00-250,=99750,例,3,、,146,31,73,75,变换计算顺序,=146,73,31,75,=2,75,31,=150,31,=150,(30+1),=4500+150,=4650,没有括号时，,可以调换乘数,或除数的位置。,102,414,157,414,157,102,=(102,102),(414,414),(157,157),=1,1,1,=1,增加去除括号,例,4,、,1248,96,24,=1248,(96,24),=1248,4,=312,1000,(125,4),=1000,125,4,=8,4,=32,除号后面,加,括号：,后面要变号，,乘号变除号 除号变乘号,除号后面,去,括号：,后面要变号，,乘号变除号 除号变乘号,例,5,、,625,25,同时乘或除,=(625,4),(,25,4),=2500,100,=25,58500,900,=(58500,100),(900,100)585,9,=65,被除数除数，,同时乘一个数,(0,除外,),，,商不变。,被除数除数，,同时除一个数,(0,除外,),，,商不变。,例,6,、,(350+165),5,除法分配,=(350,5),+(,165,5),=70,+,33,=103,(702-213-414),3,=(702,3),-,(213,3)-(414,3),=234-71-138,=25,几个数的和或差，除以一个数，可以用这几个数分别除以这个数，再求商的和。,练,习,1,、,184,17+184,83,=184,(17+83),=184,100,=18400,2,、,981+5,9810+49,981,=981+59810+49,981,=(981,1)+(981,50)+(981,49),=981,(1+50+49),=981,100,=98100,3,、,496,837-496,637,=496,(837-637),=496,200,=99200,练,习,4,、,248,69-17,248+248,48,=248,(69-17+48),=248,100,=24800,5,、,9999,7778+3333,6666,=9999,7778+3333,3,2222,=9999,7778+9999,2222,=9999,(7778+2222),=9999,10000,=99990000,6,、,(125,99+125),16,=(125,99+125,1),16,=125,(99+1),16,=12500,8,2,=1000 00,2,=200000,练,习,7,、,25,64,125,=25,(4,8,2),125,=25,4,8,125,2,=100,1000,2,=100000,2,=200000,8,、,234,1240+7660,124,=2340,124+7660,124,=(2340+7660),124,=10000,124,=1240000,9,、,56000,(14000,16),=56000,14000,16,=4,16,=64,练,习,10,、,45000,(25,90)45000,25,90,=45000,90,25,=500,25,=20,11,、,37500,4,25,=37500,(,4,25),=37500,100,=375,12,、,9600,25,=(9600,4),(,25,4),=38400,100,=384,练,习,13,、,125,91,25,=125,25,91,=5,(90+1),=450+5,=455,14,、,871,364,182,=871,(364,182),=871,2,=1742,15,、,204,312,197,312,197,204,=(204,204),(312,312),(197,197),=1,1,1,=1,练,习,16,、,(10000-1000-100-10),10,=(10000,10)-(1000,10)-(100,10)-(10,10),=1000-100-10-1,=900-10-1,=890-1,=889,17,、,(30+32+34+36+38+40),5,=(30+32+38+34+36+40),5,=(30+70+70+40),5,=(100+110),5,=20+22,=42,18,、,8,7+9,7+11,7,=(8+9+11),7,=28,7,=4,