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Bài 2:
a: \(\left(6x-39\right):7=3\)
\(\Leftrightarrow6x-39=21\)
hay x=10
53 x 29 + 47 x 29 - 53 x 21 - 47 x 21
= 29 x ( 53 + 47 ) - 21 x ( 53 + 47 )
= 29 x 100 - 21 x 100
= 100 x ( 29 - 21 )
= 100 x 8
= 800
a, 3 . 5 2 - 16 : 2 2 = 3.25 - 16:4 = 75 - 4 = 71
b, 15.141 + 59.15 = 15.(141+59) = 15.200 = 3000
c, 2 3 . 17 - 2 3 . 14 = 8.17 - 8.14 = 8.(17 - 14) = 8.3 = 24
d, 20 - 30 - 5 - 1 2 = 20 - 30 - 4 2 = 20 - (30 - 16) = 20 - 14 = 6
a, 5 . 2 2 - 18 : 3 2
= 5.4 – 18:9
= 20 – 2 = 18
b, 17.85+15.17 – 120
= 1445+255 – 120
= 1580
c, 2 3 . 17 - 2 3 . 14
= 2 3 . ( 17 - 14 ) = 8.3 = 24
d, 20 – [30 – 5 - 1 2 ]
= 20 – (30 – 16) = 6
a; 23.17 + 23.83 - 14
= 23.(17 + 83) - 14
= 8.100 - 14
= 800 - 14
= 786
b; -176 + 197 - (-76 + 97)
= -176 + 197 + 76 - 97
= -(176 - 76) + (197 - 97)
= - 100 + 100
= 0
c; 2022 - [45 - (6 - 1)2 ] + 20210
= 2022 - [45 - 52] + 1
= 2022 + 1 - [45 - 25]
= 2023 - 20
= 2003
\(\frac{-5}{23}.\frac{17}{26}+\frac{-5}{23}.\frac{9}{26}=\frac{-5}{23}.\left(\frac{17}{26}+\frac{9}{26}\right)=\frac{-5}{23}.1=\frac{-5}{23}\)
\(\frac{-21}{20}+\frac{21}{20}.\frac{3}{4}+\frac{3}{4}=\frac{21}{20}.\left(\frac{3}{4}-1\right)+\frac{3}{4}=\frac{21}{20}.\frac{-1}{4}+\frac{3}{4}=\frac{1}{4}.\left(\frac{-21}{20}+\frac{3}{4}\right)=\frac{1}{4}.\left(-\frac{3}{10}\right)=-\frac{3}{40}\)
=23(17+83)+47(71+29)
= 23.100+47.100
=100.(23+47)
=100.70=7000
23.17+47.71+83.23+47.92
=23.(17+83)+47.(29+71)
=23.100+47.100
=2300+4700
=7000