Bài 1.28 trang 22 SGK Toán 7 tập 1 KNTT

$\begin{array}{l}a)-1,2+(-0,8)+0,25+5,75-2021\\ =[-1,2+(-0,8)]+(0,25+5,75)-2021\\ =(-2)+6-2021\\ =4-2021\\ =-2017\\ b)-0,1+\frac{16}{9}+11,1+\frac{-20}{9}\\ =[(-0,1)+11,1]+\left(\frac{16}{9}+\frac{-20}{9}\right)\\ =11+\frac{-4}{9}\\ =\frac{99}{9}+\frac{-4}{9}\\ =\frac{95}{9}\end{array}$

a) –1,2 + (–0,8) + 0,25 + 5,75 – 2021

= [–1,2 + (–0,8)] + (0,25 + 5,75) – 2021

= –2 + 6 – 2021

= 4 – 2021

= –2017

b) $-0,1+\frac{16}{9}+11,1+\frac{-20}{9}$

$=\left(-0,1+11,1\right)+\left(\frac{-20}{9}+\frac{16}{9}\right)$

$=11+\frac{-4}{9}=\frac{99}{9}-\frac{4}{9}=\frac{95}{9}$