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 = \((-5).12:[(-\dfrac{1}{4})+\dfrac{1}{2}:(-2)]+1\dfrac{1}{3} = (-60):[(-\dfrac{1}{4})+\dfrac{1}{2}.(-\dfrac{1}{2})]+1\dfrac{1}{3}\)
= \((-60):[(-\dfrac{1}{4})+(-\dfrac{1}{4})]+1\dfrac{1}{3}=(-60):(-\dfrac{1}{2})+1\dfrac{1}{3}\)
= \((-60).(-2)+1\dfrac{1}{3}=121\dfrac{1}{3}\)