1、21+22+23+24+……+100
=(21+100)+(22+99)+……+(60+61)
=121+121+……+121
=121×40
=4840
2、21+23+25+27+29+31
=(21+31)×6÷2
=156
3、312+315+318+321+324
=(318-6)+(318-3)+318+(318+3)+(318+6)
=318×5
=1590
1、1+2+3+4+5+6+7+8+9+10
=(1+10)×10÷2
=55
2、1+2+3+4+5+……+20
=(1+20)×20÷2
=210
3、1+2+3+4+……+99+100
=(1+100)×100÷2
=5050
1)599996+49997+3998+407+89
=600000+50000+4000-4-3-2+407+89
=65400+487
=65887
2)(48×75×81)÷(24×25×27)
=48×75×81÷24÷25÷27
=48÷24×75÷25×81÷27
=2×3×3
=18
3)48+50+52+54+56+58+60+62
=(48+62)×8÷2
=440
1)345345÷15015
=345×1001÷(15×1001)
=345÷15×1001÷1001
=23
2)347+358+352+349
=350×4-3+8+2-1
=1400+6
=1406
3)75×45+17×25
=25×3×45+17×25
=25×(135+17)
=25×152
=25×4×38
=3800
1)654321×909090+654321×90909
=654321×999999
=654321×(100000-1)
=654321000000-654321
=654320345679
2)34×3535-35×3434
=34×35×101-35×34×101
=0
3)27000÷125
=27×1000÷125
=27×8
=216
1)222222×999999
=222222×(1000000-1)
=222222000000-222222
=222221777778
2)333333×333333
=111111×999999
=111111×(1000000-1)
=111111000000-111111
=111110888889
3)56000÷(14000÷16)
=56000÷14000×16
=4×16
=64
1)39600÷25
=396×100÷25
=396×4
=1584
2)67×21+18×21+85×79
=21×(67+18)+85×79
=21×85+85×79
=85×(21+79)
=8500
3)321×81+321×19
=321×(81+19)
=32100
1)150×40÷50
=150÷50×40
=3×40
=120
2)5600÷(25×7)
=56×100÷25÷7
=56÷7×100÷25
=32
3)210÷42×6
=210÷7÷6×6
=30
1)13×99
=13×(100-1)
=1300-13
=1287
2)75000÷125÷15
=75×1000÷125÷15
=75÷15×1000÷125
=5×8
=40
3)7900÷4÷25
=7900÷(4×25)
=79
1)125×(17×8)×4
=125×8×4×17
=1000×68
=68000
2)375×480+6250×48
=480×(375+625)
=480000
3)25×16×125
=25×2×8×125
=50000
1. 125 × (17 × 8) × 4 = 125×8×4×17 =1000×68 =68000
2. 375 × 480 + 6250 × 48 =480×(375+625)
3. 25 × 16 ×125 =25×2×8×125 =50000
4. 13 × 99 =13×(100-1) =1300-13 =1287
5. 75000 ÷ 125 ÷ 15 =75×1000÷125÷15 =75÷15×1000÷125 =5×8 =40
6. 7900 ÷ 4 ÷ 25 =7900÷(4×25) =79
7. 150 × 40 ÷ 50 =150÷50×40 =3×40 =120
8. 5600 ÷(25 ×7) =56×100÷25÷7 =56÷7×100÷25 =32
9. 210 ÷ 42 × 6 =210÷7÷6×6 =30
10. 39600 ÷ 25 =396×100÷25 =396×4 =1584
11. 67 × 21 +18 × 21 + 85 × 79 =21×(67+18)+85×79 =21×85+85×79 =85×(21+79) =8500
12. 321 × 81 + 321 × 19 =321×(81+19) =32100
15. 56000 ÷ (14000 ÷ 16) =56000÷14000×16 =4×16 =64
17. 34 × 3535 -35 × 3434 =34×35×101-35×34×101 =0
18. 27000 ÷ 125 =27×1000÷125 =27×8 =216
20. 347 + 358 + 352 + 349 =350×4-3+8+2-1 =1400+6 =1406
21. 75 × 45 + 17 × 25 =65400+487 =65887
23. (48 × 75 ×81)×((24 ×
1)125 ×(17 × 8)× 4
= 125×8×4×17
=1000×68
=68000
2)375 × 480 + 6250 × 48
=480×(375+625)
3)25 × 16 ×125
=25×2×8×125
=50000
4)13 × 99
=13×(100-1)
=1300-13
=1287
5)75000 ÷ 125 ÷ 15
=75×1000÷125÷15
=75÷15×1000÷125
=5×8
=40
6)7900 ÷ 4 ÷ 25
=7900÷(4×25)
=79
7)150 × 40 ÷ 50
=150÷50×40
=3×40
=120
8)5600 ÷(25 ×7)
=56×100÷25÷7
=56÷7×100÷25
=32
9)210 ÷ 42 × 6
=210÷7÷6×6
=30
10)39600 ÷ 25
=396×100÷25
=396×4
=1584
11)67 × 21 +18 × 21 + 85 × 79
=21×(67+18)+85×79
=21×85+85×79
=85×(21+79)
=8500
12)321 × 81 + 321 × 19
=321×(81+19)
=32100
15)56000 ÷ (14000 ÷ 16)
=56000÷14000×16
=4×16
=64
17)34 × 3535 -35 × 3434
=34×35×101-35×34×101
=0
18)27000 ÷ 125
=27×1000÷125
=27×8
=216
20)347 + 358 + 352 + 349
=350×4-3+8+2-1
=1400+6
=1406
21)75 × 45 + 17 × 25
=65400+487
=65887
23)(48 × 75 ×81)÷(24 × 25 × 27)
=48 × 75 ×81÷24÷25÷27
=48÷24×75÷25×81÷27
=2×3×3
=18