(5,3 - 2,8) - (4 + 5,3)

= 2,5 - 9,3

= -6,8

\(\left(5,3-2,8\right)-\left(4+5,3\right)\)

\(=2,5-9,3\)

\(=-6,8\)

a) \(=\left(278+622\right)+\left(809-209\right)=900+600=1500\)

b) \(=64.57+64.43-2300=64\left(57+43\right)-2300=54.100-2300=5400-2300=3100\)

a) 278+809+622-209
  = (278+622)+(809-209)
  =       900    +    600
  =              1500
b) 64.57+64.43-2300
  = 64(57+43)-2300
  = 64.100-2300
  = 6400-2300=4100
c) 24.5-[131-(13-4)2]
  = 24.5-(131-9.2)
  = 120-113= 7

=80-(100-24)

=80-76

=4 

80-( 4.25-3.8)

=80-(100-24)

=80-100+24

=-20+24

=4

Lời giải:

$A=(-1-2+3+4)+(-5-6+7+8)+(-9-10+11+12)+...+(-2021-2022+2023+2024)-2024$

$=\underbrace{4+4+...+4}_{506}-2024$
$=4.506-2024=0$

a) \(255+312+188+645\)

\(=\left(255+645\right)+\left(312+188\right)\)

\(=900+500\)

\(=1400\)

b) \(25+12\cdot5-60\)

\(=25+60-60\)

\(=25\)

c) \(12\cdot75+12\cdot7+12\cdot18\)

\(=12\cdot\left(75+7+18\right)\)

\(=12\cdot100\)

\(=1200\)

d) \(2^4\cdot5-\left[131-\left(13-4\right)^2\right]\)

\(=16\cdot5-\left(131-9^2\right)\)

\(=80-\left(131-81\right)\)

\(=80-50\)

\(=30\)

4 : 8 x (1,5 + 0,9) = 0,5 x (1,5 + 0,9)

                          = 0,5 x 2,4

                          = 1,2

ssh = (100 - 2) : 2 + 1 = 50 (số hạng)

=> B = (100 + 2) x 50 : 2 = 2550