giúp mình vs 1h30 mình đi hc r
Bài 2:
a) \(\dfrac{4}{5}+\dfrac{-5}{4}\)
\(=\dfrac{16}{20}+\dfrac{-25}{20}\)
\(=\dfrac{-9}{20}\)
b) \(\dfrac{-1}{3}+\dfrac{2}{5}-\dfrac{5}{6}\)
\(=\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}\)
\(=\dfrac{-23}{30}\)
c) \(\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}\)
\(=\dfrac{2}{3}-\dfrac{5.14}{7.25}\)
\(=\dfrac{2}{3}-\dfrac{70}{175}\)
\(=\dfrac{2}{3}-\dfrac{2}{5}\)
\(=\dfrac{10}{15}-\dfrac{6}{15}\)
\(=\dfrac{4}{15}\)
Bài 1:
\(a,\dfrac{15}{60}=\dfrac{15:15}{60:15}=\dfrac{1}{4}\)
\(b,\dfrac{42}{-28}=\dfrac{-42}{28}=\dfrac{-42:14}{28:14}=\dfrac{-3}{2}\)
\(c,\dfrac{24.39}{15.48}=\dfrac{1.39}{15.2}=\dfrac{39}{30}\)
\(d,\dfrac{49.2+49.3}{49.15}=\dfrac{49.\left(2+3\right)}{49.15}=\dfrac{49.5}{49.15}=\dfrac{1.1}{1.3}=\dfrac{1}{3}\)
\(e,\dfrac{\left(-13\right).24.\left(-20\right)}{\left(-26\right).8.15}=\dfrac{1.3.\left(-4\right)}{2.1.3}=\dfrac{1.1.\left(-2\right)}{1.1.1}=-2\)
\(f,\dfrac{53.19-53}{19-72}=\dfrac{53.\left(19-1\right)}{-53}=\dfrac{53.18}{-53}=\dfrac{1.18}{-1}=-18\)
\(g,\dfrac{-12.13+12.24}{9.17-9.5}=\dfrac{-12\left(13-24\right)}{9.\left(17-5\right)}=\dfrac{-12.\left(-11\right)}{9.12}=\dfrac{-1.\left(-11\right)}{9.1}=\dfrac{11}{9}\)
\(h,\dfrac{2^{20}.125}{2^{24}.50}=\dfrac{-8.3}{2}=\dfrac{-4.3}{1}=-12.\)
Bài 2:
\(a,\dfrac{4}{5}+\dfrac{-5}{4}=\dfrac{16}{20}+\dfrac{-25}{20}=\dfrac{-9}{20}\)
\(b,\dfrac{-1}{3}+\dfrac{2}{5}-\dfrac{5}{6}=\dfrac{-10}{30}+\dfrac{12}{30}-\dfrac{25}{30}=\dfrac{-23}{30}\)
\(c,\dfrac{2}{3}-\dfrac{5}{7}.\dfrac{14}{25}=\dfrac{2}{3}-\dfrac{2}{5}=\dfrac{10}{15}-\dfrac{6}{15}=\dfrac{4}{15}.\)
