Bài 7:
1)35. 18 – 5. 7. 28
=35.18-35.28
=35.(18-28)
=35.(-10)
=-350
2)45 – 5. (12 + 9)
=45-(5.12+5.9)
=45-(60+45)
=45-60-45
=(45-45)-60
=0-60
=-60
3)24. (16 – 5) – 16. (24 - 5)
=24.16-24.5-16.24+16-5
=(24.16-16.24)+(-24.5+16.5)
=0+(-24.5+16.5)
=-24.5+16.5
=5.(-24+16)
=5.(-8)
=-40
4)29. (19 – 13) – 19. (29 – 13)
=29.19-29.13-19.29+19.13
=(29.19-19.29)+(-29.13+19.13)
=0+(-29.13+19.13)
=-29.13+19.13
=13.(-29+19)
=13.(-10)
=-130
5)31. (-18) + 31. ( - 81) – 31
=31.[-18+(-81)-1]
=31.(-100)
=-3100
6)(-12).47 + (-12). 52 + (-12)
=-12.(47+52+1)
=-12.100
=-1200
7)13.(23 + 22) – 3.(17 + 28)
=13.45-3.45
=45.(13-3)
=45.10
=450
8)-48 + 48. (-78) + 48.(-21)
=48.(-1)+48.(-78)+48.(-21)
=48.[-1+(-78)+(-21)]
=48.(-100)
=-4800
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