小学数学 小学数学三年级奥数(从课本到奥数_第一学期) (2)(1)

=3939 11 22×99 =22×（100-1） =22×100-22×1 =2200-22 =2178 12 1+3+5+7+9+11+13+15+17+19 =(1+19)+(3+17)+(5+15)+(7+13)+(9+11) =20+20+20+20+20 =100 13 1350+49+68+51+32+1650 =(1350+1650)+(49+51)+(68+32) =3000+100+100 =3200 14 875-364-236 =875-(364+236) =875-600 =275 15 1847-1928+628-136-64 =1847-(1928-628)-(136+64) =1847-1300-200 =347 16 2+4+6+8+……+100-1-3-5-7-……-97-99 =2-1+4-3+6-5+……+98-97+100-99 =(2-1)+(4-3)+……+(98-97)+(100-99) =50×1 =50 17 78+76+83+82+77+80+79+85 =80×8-2-4+3+2-3-1+5 =640 18 102+105+99+101+98 =100×5+2+5-1+1-2 =500+5 =505 19 2+4+6+8+10+12+14+16+18+20 =(2+20) ×10÷2 =（2+20）×5 =110 20 128+186+72-86 =128+72+186-86 =(128+72)+(186-86) =200+100 =300 21 324-(124-97)
= 8732-2000-8 = 6732-8 = 6724 74 487―298 = 487-300+2 = 187+2 = 189 75 402+307―297―99 = 400+300-300-100+2+7+3+1 = 300+13 = 313 76 307+201―398―99 = (300+200-400-100)+(7+1+2+1) = 0+11 = 11 77 208+494―498―95 = (200+500-500-100)+(8-6+2+5) = 100+9 = 109 78 99999+9999+999+99+9 =(100000+10000+1000+100+10)-1-1-1-1-1 = 111110-5 = 111105 79 375+283+225+17 = (375+225)+(283+17) = 600+300 =900 80 321+127+79+73 = (321+79)+(127+73) = 400+200 = 600 81 237+(163-37) = 237-37+163 = 200+163 = 363 82 375+(125-47) = (375+125)-47 = 500-47 = 453 83 812+(188-123) = (812+188)-123 = 1000-123 = 877
=(894-94)-(89+111)-(95+105)
=800-200-200
=400
49 567+231-267+269
=(567-267)+(231+269)
=300+500
=800
50 2000-99-9-98-8-97-7-96-6-95-5-94-4-93-3-92-2-91-1
=2000-(99+9+98+8+97+7+96+6+95+5+94+4+93+3+92+2+91+1)
=4050
43 1272-995
=1272-(1000-5)
=1272-1000+5
=277
44 478-128+122-72
=(478+122)-(128+72)
=600-200
=400
45 464-545+99+345
=464-(545-345)+100-1
=464-200+100-1
=ቤተ መጻሕፍቲ ባይዱ63
32 1361+972+639+28 =(1361+639)+(972+28) =2000+1000 =3000 33 188+873 =(188+12)+(873-12) =200+861 =1061 34 548+996 =(548-4)+(996+4) =544+1000 =1544 35 9898+203 =(9898+102)+(203-102) =10000+101 =10101 36 536+(541+464)+459 =(536+464)+(541+459) =2000 37 588+264+148 =588+(12+252)+148 =(588+12)+(252+148) =600+400 =1000 38 8996+3458+7546 =(8996+4)+(3454+7546) =9000+11000 =9000+11000 =20000(3458 分成 4 和 3454) 39 567+558+562+555+563 =560×5+(7-2+2-5+3) =2800+5 =2805 40 1870-280-520 =1870-(280+520) =1870-800 =1070 41 4995-(995-480) =4995-995+480 =4000+480 =4480 42 4250-294+94 =4250-(294-94) =4250-200
46 537-(543-163)-57
=537-543+163-57
=(537+163)-(543+57)
=700-600
=100
47 947+(372-447)-572
=947+372-447-572
=(947-447)-(572-372)
=500-200
=300
48 894-89-111-95-105-94
1 19+199+1999+19999 =20+200+2000+20000-1-1-1-1 =22220-4 =22216 2 1999+198+97+6 =(1999+1)-1+(198+2)-2+(97+3)-3+6 =2000+200+100+(6-1-2-3) =2300+0 =2300 3 836+501-498+305 =836+(501-1)+1-(498+2)+2+(305-5)+5 =836+500-500+300+（1+2+5） =1136+8 =1144(注意:把减去 498 变为减去 500 时,多减了 2,所以后面要加上 2。) 4 492-193+93 =492-(193-93) =492-100 =392 5 48-47+46-45+44-43+42-41 =(48-47)+(46-45)+(44-43)+(42-41) =1+1+1+1 =4 6 5+6+7+8+9+10+11+12+13+14+15 =(5+15)×11÷2 =20×11÷2 =20÷2×11 =10×11 =110 7 25×55×4 =25×4×55 =100×55 =5500 8 25×32×125×7 =25×4×（8×125）×7 =100×1000×7 =700000 9 25×（40+4） =25×40+25×4 =1000+100 =1100 10 39×101 =39×（100+1） =39×100+39×1 =3900+39
=1800-100-200 =1500 63 125×13×4×8×25×5×2 =（125×8）×（25×4）×（5×2）×13 =1000×100×10×13 =13000000 64 1999+999×999 =1000+999+999×999 =1000+999×（1+999） =1000+999×1000 =1000×(1+999) =1000×1000 =1000000 65 321×654÷987÷654×987÷321 =（321÷321）×（654÷654）×（987÷987） =1×1×1 =1 66 1-2+3-4+5-6+…+1991-1992+1993 =1+(3-2)+(5-4)+…+(1991-1990)+(1993-1992) =1+1×996 =997 67 947+(372-447)-572 =947+372-447-572 =(947-447)-(572-372) =500-200 =300 68 456×2×125×25×5×4×8 =456×(2×5)×(25×4)×(125×8) =456000000 69 750+1002 = (750+2)+1000 = 1752 70 2004+271 = 2000+(271+4) = 2275 71 574-397 = 574-400+3 = 174+3 = 177 72 472―203 = 472-200-3 = 272-3 = 269 73 8732―2008
=1
52 198+96+297+10
=200+100+300-2-4-3+10
=600-9+10
=601
53
895-504-97
=（900-5）-（500+4）-（100-3） =900-5-500-4-100+3 =300-5-4+3 =300-6 =294 54 102+101+98-96-97-105 =102+101+98-96-97-3-102 =102+101 +(98-96)-(97+3)-102 =101+2-100 =3 55 195+196+197+198+199 =200+200+200+200+200-5-4-3-2-1 =1000-15 =985 56 89+899+8999+89999+899999 =90+900+9000+90000+900000-1-1-1-1-1 =999990-5 =999985 57 123 + 234 + 345 - 456 + 567 - 678 + 789 =123+234+345+(567-456)+(789-678) =234×3+111+111 =702+222 =924 58 37+56+63+44 =(37+63)+(56+44) =100+100 =200 59 284+178 =(300-16)+(200-22) =(300+200)-(16+22) =500-38 =462 60 89+91+90+92+88+87+93+92+87 =(90-1)+(90+1)+90+(90+2)+(90-2)+(90-3)+(90+3)+(90+2)+(90-3) =90×9-1+1+2-2-3+3+2-3 =810-1 =809 61 4996+3993+2992+1991+98 =(5000-4)+(4000-7)+(3000-8)+(2000-9)+(100-2) =5000+4000+3000+2000+100-4-7-8-9-2 =14100-30 =14070 62 1800-90-176-10-24 =1800-(90+10)-(176+24)
=2000-[(99+1)+(98+2)+(97+3)+(96+4)+(95+5)+(94+6)+(93+7)+(92+8)+(91+9)]
=2000-900
=1100
51 1+2-3-4+5+6-7-8+9+……+1998-1999-2000+2001
=1+(2-3-4+5)+(6-7-8+9)+……+(1998-1999-2000+2001)
=324-124+97 =200+97 =297 22 283+(385-183) =283+385-183 =283-183+385 =100+385 =485 23 286+879-679 =286+（879-679） =286+200 =486 24 812-593+193 =812-（593-193） =812-400 =412 25 4+8+12+16+20 =(4+16)+(8+12)+20 =20×3 60 26 20×37×5 =20×5×37 =100×37 =3700 27 4×45×25 =4×25×45 =100×45 =4500 28 125×5×8 =125×8×5 =1000×5 =5000 29 72×9÷8 =72÷8×9 =9×9 =81 30 36+87+64 =(36+64)+87 =100+87 =187 31 99+136+101 =(99+101)+136 =200+136 =336