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1) 38 + ( - 40 ) + 24
= 62 + (-40)
= 62 - 40
= 22
2) - 28 - ( - 12 ) + ( - 35 ) + 24
= -4 - ( - 12) + ( - 35)
= -4 + 12 - 35
= - 39 + 12
= - 27
38 + ( - 40 ) + 24
= ( 38 + 24 ) + ( - 40 )
= 62 + ( - 40 )
= 62 - 40
= 22
- 28 - ( - 12 ) + ( - 35 ) + 24
= - ( 28 - 12 ) + - ( 35 - 24 )
= - 16 + ( - 11 )
= - 27
1/
$M=\frac{1}{3.8}+\frac{1}{8.13}+\frac{1}{13.18}+....+\frac{1}{33.38}$
$5M=\frac{8-3}{3.8}+\frac{13-8}{8.13}+\frac{18-13}{13.18}+...+\frac{38-33}{33.38}$
$=\frac{1}{3}-\frac{1}{8}+\frac{1}{8}-\frac{1}{13}+\frac{1}{13}-\frac{1}{18}+....+\frac{1}{33}-\frac{1}{38}$
$=\frac{1}{3}-\frac{1}{38}=\frac{35}{114}$
$\Rightarrow M=\frac{35}{114}:5=\frac{7}{114}$
2/
$N=\frac{1}{3.10}+\frac{1}{10.17}+\frac{1}{17.24}+\frac{1}{24.31}+\frac{1}{31.38}$
$7N=\frac{10-3}{3.10}+\frac{17-10}{10.17}+\frac{24-17}{17.24}+\frac{31-24}{24.31}+\frac{38-31}{31.38}$
$=\frac{1}{3}-\frac{1}{10}+\frac{1}{10}-\frac{1}{17}+\frac{1}{17}-\frac{1}{24}+\frac{1}{24}-\frac{1}{31}+\frac{1}{31}-\frac{1}{38}$
$=\frac{1}{3}-\frac{1}{38}=\frac{35}{114}$
$\Rightarrow N=\frac{35}{114}:7=\frac{5}{114}$
a, 24 x 91 + 6 x 47 - 24 x 38
= (24 x 91 - 24 x 38) + 6 x 47
= 24 x (91 - 38) + 6 x 47
= 24 x 53 + 6 x 47
= 1272 + 282
= 1554
( 5x - 24 ) x 38 = 2 x 311
5x - 16 = 2 x 311 : 38
5x - 16 = 2 x 33
5x - 16 = 2 x 27
5x - 16 = 54
5x = 54 + 16
5x = 70
x = 70 : 5
x = 14
Vậy x = 14
Lời giải:
$(5x-2^4).3^8=2.3^{11}$
$5x-16=2.3^{11}:3^8=2.3^3=2.27=54$
$5x=54+16=70$
$x=70:5=14$
-62
- 62