Giải bài 1 trang 88 - Sách giáo khoa Toán 7 tập 2

Đề bài

 Thực hiện các phép tính:

a) \(9,6.2\dfrac{1}{2}-(2.125-1\dfrac{5}{12}):\dfrac{1}{4}\)

b) \(\dfrac{5}{18}-1,456:\dfrac{7}{25}+4,5.\dfrac{4}{5}\)

c) \((\dfrac{1}{2}+0,8-1\dfrac{1}{3}).(2,3+4\dfrac{7}{25}-1,28)\)

d) \((-5).12:[(-\dfrac{1}{4})+\dfrac{1}{2}:(-2)]+1\dfrac{1}{3} \)

Hướng dẫn giải

a) Đặt A = \(9,6.2\dfrac{1}{2}-(2.125-1\dfrac{5}{12}):\dfrac{1}{4}=9,6.\dfrac{5}{2}-(250-\dfrac{17}{12}).4\)

              = \(24 - \dfrac{2983}{12}.4\) = \(24 - \dfrac{2983}{3}=\dfrac{-2911}{3}\)

b) Đặt B = \(\dfrac{5}{18}-1,456:\dfrac{7}{25}+4,5.\dfrac{4}{5}=\dfrac{5}{18}-1,456.\dfrac{25}{7}+3,6\)

              = \(\dfrac{5}{18}-5,2+3,6\) = \(\dfrac{5}{18}-1,6\) = \(\dfrac{-119}{90}\) = \(-1\dfrac{29}{90}\)

c) Đặt C = \((\dfrac{1}{2}+0,8-1\dfrac{1}{3}).(2,3+4\dfrac{7}{25}-1,28)\)

              = \((\dfrac{1}{2}+\dfrac{8}{10}-\dfrac{4}{3}).(\dfrac{23}{10}+\dfrac{107}{25}-\dfrac{128}{100})\)

              = \(\dfrac{15+24-40}{30}.\dfrac{115+214-64}{50}\)

              = \(\dfrac{-53}{300}\)

d) Đặt D = \((-5).12:[(-\dfrac{1}{4})+\dfrac{1}{2}:(-2)]+1\dfrac{1}{3} = (-60):[(-\dfrac{1}{4})+\dfrac{1}{2}.(-\dfrac{1}{2})]+1\dfrac{1}{3}\)

= \((-60):[(-\dfrac{1}{4})+(-\dfrac{1}{4})]+1\dfrac{1}{3}=(-60):(-\dfrac{1}{2})+1\dfrac{1}{3}\) 

= \((-60).(-2)+1\dfrac{1}{3}=121\dfrac{1}{3}\)