=(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+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
=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
=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
=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
=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
=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
=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
=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
=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