1、 3.注意构造,让算式满足乘法分配律的条件。103-2- 2.69.9 四、借来还去法看到名字,就知道这个方法的含义。用此方法时,需要注意观察,发现规律。还要注意还哦 ,有借有还,再借不难嘛。9999+999+99+9 4821-998 5、拆分法顾名思义,拆分法就是为了方便计算把一个数拆成几个数。这需要掌握一些“好朋友”,如:2和5,4和5,2和2.5,4和2.5,8和1.25等。分拆还要注意不要改变数的大小哦。四运算定律加法交换律:ab = ba加法结合律:(ab)c = a(bc)乘法交换律:b = ba乘法结合律:(ab)c = a乘法分配律:(ab)cb (ab)cb五其它性质abc
2、 = acb 可以变化顺序abc = a(bc) 可以加起来一起减a(bc)= abc 括号前是减号,去掉后变符号a(bc)= abc 括号前是加号,去掉后不变符号c = ab 可以变化顺序c) 可以乘起来一起除abc = acb 可以变化顺序六、总结1、在简便运算中,运算定律的区别和适用范围最重要,通常情况下,交换律和结合律只适用于同种运算或者同级运算,在交换的时候要注意连同前面的符号一起交换;2、在减法和除法的性质中,括号外面和里面必须是同级运算才可以用,如果括号前面是减法,括号里面有加法和减法,去括号以后里面的每一个数前面的符号都要改变;如果括号前面是除号,括号里面有乘法和除法,去括号以
3、后每一个数前面的符号都要改变;3、对于分配律,如果被除数是几个数的和或者差,除数是某一个数,可以用分配律,如果除数是几个数的和或者差,不能用分配律;4、两种运算技巧:(1)凑数:把一个数写成是一个与它相近的整十、整百或者整千数与一个较小的数的和或者差,在运用运算定律达到简便运算的效果;(2)拆数:把一个合数分解质因数,写成几个数的积,然后在运用乘法的运算定律,达到简便运算的目的。四年级数学简便计算题第一类:加 65+73+135 357+288+143 272+68+28 129+235+171+165 17+145+23+35 999+99+9+36+7+8+102+103+104 9998
4、+3+99+998+3+9 第二类:减 400-256-44 517-53-47 284-159-41 258-42-16 545-167-145 478-47-178 344-(144+37) 236-(177+36) 第三类:乘 4545 23 52 2594 8(12513) (250125)(48) 88125 72125 1256425 421255 2588125 第四类:(12+50)40 125(40-4) 76103 18125 2544 4225 999 9978 第五类:37+3755 2821+2879 1723-237 3846+6438 9932+32 46+465
5、9 1672+1673+1675 398+639-3928225-2225-6225 (42+25)125+(18+15)2324+252+2718+251 9922+3334 第六类:除 36049 25052 600128008 48048 24012 42035 240025 780012 第七类:加减 92+99 197+102 354-108 405-99 127-98 323+189-123 248+86-48 672-36+64 (6467-832)+(1832-1467) 1530+(592-530)-192 (2+4+6+98+100)-(1+3+5+97+99) 第八类:乘
6、除 9604648 9900012111 3702381234 640(164) 1000(1254)第九类:加减乘除 (98+147)49 (230-23)23 (250-25)25 173628+106428 125(860+24012) 700+61212(37+15)85+1360 200520062006-200620052005 425 25(40-4) 869 9978 4538+3855 79 377 3838 59 1675394 28225 (42+25)125 65+73+135 357+288+143 272+68+28 129+235+171+165 17+145+2
7、3+35 400-256-44 517-53-47 284-159-41 258-42-16 545-167-145 478-47-178 344-(144+37) 236-(177+36) 452 4 88) 88125 72125 125425 25125 (12+50)40 103 18 2544 4225 999 9955 2879 1738 9932+32 46+464 3602505 8008 48048 24012 42035 117+392+608 88272787538747 775725 2346634 5285347 435(135189) 16725322525 993
8、8 14714799 25(48) 10875 35201 7598 74 26 253288 2548 3500420352 3025570 28241159 12 6.3 1.8 12564+12536 19964 5285347 158395105 480025 (136)6) 2.1 99 2.1 0.18 4.26 0.18 4.26 810075 16800120 124824 315015 (10000-1000-100-10)10 13829362107 99+999+9999+99999 66.868.661.34 881189 10 0.432 2.568 9819925
9、6.8 0.04 355+260+140+245 10299 2645-180-245 12532 2546 10156 9926 382101-382 60508 930 0.6 5 1022478422 63.4 2.5 0.4 2357183317357 6723664 36643664 50025734143 755-287+871814378422 899989 3999+498 22522512 6982919 568(68178) 3821653582 1552564598 759-126-259 216+89+11 7599+275 1050157 72002430 219 9
10、9 58 101 76 102 7846+7854 16912323169 129101129 5651+5648+56 12532 24514+189214 732254332 562474+2624 228+(72+189) 109+(291176)(375+1034)+(966+125) (2130+783+270)+1017 参考答案65+73+135 357+288+143 272+68+28 =65+135+73 =357+143+288 =272+28+68=273 =788 =368=129+171+(235+165) =17+23+(145+35) =999+1+(99+1)
11、+(9+1)=700 =220 =1110=102+8+(7+103)+(6+104) =9998+2+(99+1)+(998+1)+(9+1)=330 =11110=400-(256+44) =517-(53+47) = 284-(156+41)=100 =417 =84 =258-(42+16) =545-145-167 =478-178-47=200 =233 =233=244-144-37 =236-36-177=63 =23=455) =23(52) =259=90 =230 =9008) 88=813 =125(2504) =811=13000 =1000000 =1100025
12、429 =125(258) =428)=9000 =200000 = 210000=100(8125) =1100000=1240+5040 =12540-1254 =76(100+3)=880 =5400 =76100+763 =7828125 2525 99=(10+8)125 =2511 =221 =10125+8125=2250 =110 =1050=(100-1) 7878-178 =7722=37+(45+55) =28(21+79) =23(17-7)=3700 =2800 =230=38(46+64) =32(99+1) = 46(59+1)110 =3200 =2760(10
13、0+10)100+3810=4180=167(2+3+5) =39(8+6-4)=1670 =390=225(28-2-6) =125(42+18+25+15)=4500 =12500(23+25+27) =33(66+34)=600 =3300=3609) = 2502) =600(125)=10 =25 =10=80085 =480485 =240=20 =2 =435 2400=42075 =24005 =780062=12 =96 =650=92+(100-1) =197+(100+2) =354-(100+8)=92+100-1 =197+100+2 =354-100-8=191 =
14、299 =246405-99 127-98 323+189-123 =405-(100-1) =127-(100-2) =323-123+189= 405-100+1 =127-100+2 =389=306 =29=248-48+86 =672-(36+64) =6467-1467+(1832-832)= 286 =572 =6000 1530+(592-530)-192 (2+4+6+98+100)-(1+3+5+97+99) =1530-530+(592-192) =(2-1)+(4-3)+(98-97)+(100-99)=1400 =1+1+.+1+1 =50=9604846 =9900
15、0(12111) =123431234=920 =9000 =114 4) 1000=640164 =10004=160 =32=9849+14749 =23023-2323 =25025-2525=5 =9 =928 125=(1736+1064) 28 =125880 =700+6123=100 =125110 =700+204 =110000 =90485+1360 2005 =5085+285+1360 =2005200610001-2006200510001=4250+170+1360 =0=5610+170=5780=125(425) =10011125)=210000 =1100
16、0004 =86=680 =4500 =86100+863=8858=(10+8) 2110+1258 =1100 =1050=22509 =(100-1) 78 =(45+55) 389-9 =78100-78 =3800 =91 =7722=(21+79) 79 =(37-7) 23 =(46+64) =7900 =690 =380059 167=(99+1) 32 =(59+1) 59 =(2+3+5) 167=3200 =3540 =16704 28=(8+6-4) 39 =(28-2-6) 225=390 =2500=(42+18)+(25+15) 125 =65+135+73 =3
17、57+143+288=12500 =273 =788272+68+28 129+235+171+165 17+145+23+35 =272+28+68 =129+171+(235+165) =17+23+(145+35)=368 =700 =220=400-(256+44) =517-(53+47) =284-(159+41)=100 =417 =84=545-145-167 =478-178-47 =344-144-37=233 =253 =163=236-36-177 =452)=23 =90 =230 4 8=259 =813 =250=900 =13000 =1000000125 72=11125) =9125) =12525)=11000 =9000 =100000=42125) =100125) =1240=210000 =1100000 =2480(100+3) =(10+8) =4500 =76100+376 =10 =7828 =2250(40+4) =(40+2) 25 =(100-1) 40+254 =4025+225 =9100-9 =7800-78=1100 =1050 =891 =7722=(45+55) 37 =(21+79) 79 =(17-7)
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