Bài 1.28 trang 22 SGK Toán 7 tập 1 KNTT

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

Thanks nhé

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

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

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