Tính nhanh:
a) \(\frac{7}{20}+\frac{-10}{18}+\frac{-4}{9}+\frac{16}{20}\)
b) \(\frac{1}{2}+\frac{-1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{-1}{4}+\frac{1}{3}+\frac{-1}{2}\)
Hướng dẫn giải
a) \(\frac{7}{20}+\frac{-10}{18}+\frac{-4}{9}+\frac{16}{20}=\left(\frac{7}{20}+\frac{16}{20}\right)+\left(\frac{-10}{18}+\frac{-4}{9}\right)\)
\(=\frac{23}{20}+\left(\frac{-5}{9}+\frac{-4}{9}\right)\)\(=\frac{23}{20}+\frac{-20}{20}=\frac{3}{20}\)
b) \(\frac{1}{2}+\frac{-1}{3}+\frac{1}{4}+\frac{1}{5}+\frac{-1}{4}+\frac{1}{3}+\frac{-1}{2}\)
\(=\left(\frac{1}{2}+\frac{-1}{2}\right)+\left(\frac{-1}{3}+\frac{1}{3}\right)+\left(\frac{-1}{3}+\frac{1}{3}\right)+\frac{1}{5}\)
\(=0+0+0+\frac{1}{5}\)
\(=\frac{1}{5}\)
Học bài
