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a ) 4 7 + 2 7 + 1 7 + 3 4 + 5 4 = 3 b ) − 5 7 + − 2 7 + − 1 5 + 3 4 + 1 4 = − 1 5
c ) 5 13 + 8 13 + − 5 7 + − 20 41 + − 21 41 = − 5 7 d ) 1 28 + 3 28 + 3 14 + − 1 14 + − 1 7 = 1 7 e ) 1 2 + − 1 2 + − 2 3 + 2 3 + 3 4 + − 3 4 + − 4 5 + 4 5 + 5 6 + − 5 6 = 0
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a) 320 x 63 - 16 x 20 + 32 x 370
= 320 x 63 - 320 x + 320 x 37
= 320 x ( 63 - 1 + 37 )
= 320 x 99
= 320 x ( 100 - 1 )
= 320 x 100 - 320
= 32000 - 320 = 31 680
b) 35 x 61 + 215 x 5 + 35 x 39 + 57 x 25
= 5 x 427 + 5 x 215 + 5 x 273 + 5 x 285
= 5 x ( 427 + 215 + 273 + 285 )
= 5 x 1200 = 6000
c) 34 x 24 - 94 x 6 + 83 x 48 - 47 x 88
= 204 x 4 - 4 x 141 + 996 x 4 - 1034 x 4
= 4 x ( 204 - 141 + 996 - 1034 )
= 4 x 25 = 100
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a) (-30) + 17 + (-70) + 33
=[-30+(-70)]+(17+33)
=-100+50
=-50
b) 56 - 15 - 6 + (-75)
=(56-6)-[15+(-75)]
=50-(-60)
=110
c) (157 - 56) - (44 + 57)
=157-56-44+57
=(-157-57)-(56+44)
=-100-100
=-200
d) (-24 + 174) - (174 - 24)
=-24+174-174+24
=(-24+24)+(174-174)
=0+0
=0
e) (35 - 47) - (-123 + 35) + [20 - (123 - 57)]
=35-47+123-35+[20-123+57]
=35-47+123-35+20-123+57
=(35-35)+(123-123)+(-47+57)
=0+0+(-10)
=-10
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A = 1/2 + 1/6 + 1/12 + 1/20 + 1/30 + 1/42 + 1/56 + 1/72
= 1/1.2 + 1/2.3 + 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9
= 1- 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + 1/4 - 1/5 + 1/5 - 1/6 + 1/6 - 1/7 + 1/7 - 1/8 + 1/8 - 1/9
= 1 - 1/9 = 8/9
Câu B, C dấu * là nhân hay công vậy?
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a. ( - 57 ) . ( 67 - 34 ) - 67 . (34 -57 )
= - 57 . 67 - ( - 57 ) . 34 - 67 . 34 - 67 . 57
= 57 . ( 67 - 67 ) + 34 . ( 67 - 57 )
= 57 . 0 + 34 . 10
= 0 + 340
= 340
\(57\cdot25+57:\frac{1}{35}+114\cdot20\)
\(=57\cdot25+57\cdot35+2\cdot57\cdot20\)
\(=57\cdot\left(25+35+2\cdot20\right)\)
\(=57\cdot\left(25+35+40\right)\)
\(=57\cdot100\)
\(=5700\)
\(=57.25+57.35+57.2.20\)
\(=57.\left(25+35+60\right)\)
\(=57.100=5700\)