Bài 2:
a: \(\dfrac{12}{7}=\dfrac{12\cdot2}{7\cdot2}=\dfrac{24}{14};\dfrac{2}{2}=\dfrac{2\cdot7}{2\cdot7}=\dfrac{14}{14}\)
\(\dfrac{4}{7}=\dfrac{4\cdot2}{7\cdot2}=\dfrac{8}{14};\dfrac{9}{14}=\dfrac{9\cdot1}{14\cdot1}=\dfrac{9}{14}\)
mà \(\dfrac{24}{14}>\dfrac{14}{14}>\dfrac{9}{14}>\dfrac{8}{14}\)
nên \(\dfrac{12}{7}>\dfrac{2}{2}>\dfrac{9}{14}>\dfrac{4}{7}\)
b: \(\dfrac{2}{5}=\dfrac{2\cdot3}{5\cdot3}=\dfrac{6}{15};\dfrac{13}{15}=\dfrac{13\cdot1}{15\cdot1}=\dfrac{13}{15};\dfrac{19}{15}=\dfrac{19\cdot1}{15\cdot1}=\dfrac{19}{15}\)
\(\dfrac{2}{3}=\dfrac{2\cdot5}{3\cdot5}=\dfrac{10}{15}\)
mà \(\dfrac{19}{15}>\dfrac{13}{15}>\dfrac{10}{15}>\dfrac{6}{15}\)
nên \(\dfrac{19}{15}>\dfrac{13}{15}>\dfrac{2}{3}>\dfrac{2}{5}\)
c: \(\dfrac{2}{3}=\dfrac{2\cdot6}{3\cdot6}=\dfrac{12}{18};\dfrac{1}{2}=\dfrac{1\cdot9}{2\cdot9}=\dfrac{9}{18}\)
\(\dfrac{11}{18}=\dfrac{11}{18};\dfrac{5}{9}=\dfrac{5\cdot2}{9\cdot2}=\dfrac{10}{18}\)
mà \(\dfrac{12}{18}>\dfrac{11}{18}>\dfrac{10}{18}>\dfrac{9}{18}\)
nên \(\dfrac{2}{3}>\dfrac{11}{18}>\dfrac{5}{9}>\dfrac{1}{2}\)
d: \(\dfrac{1}{2}=\dfrac{1\cdot8}{2\cdot8}=\dfrac{8}{16};\dfrac{3}{8}=\dfrac{3\cdot2}{8\cdot2}=\dfrac{6}{16}\)
\(\dfrac{5}{4}=\dfrac{5\cdot4}{4\cdot4}=\dfrac{20}{16};\dfrac{7}{16}=\dfrac{7}{16}\)
mà \(\dfrac{20}{16}>\dfrac{8}{16}>\dfrac{7}{16}>\dfrac{6}{16}\)
nên \(\dfrac{5}{4}>\dfrac{1}{2}>\dfrac{7}{16}>\dfrac{3}{8}\)
e: \(\dfrac{13}{20}=\dfrac{13}{20};\dfrac{3}{5}=\dfrac{3\cdot4}{5\cdot4}=\dfrac{12}{20};\dfrac{7}{10}=\dfrac{7\cdot2}{10\cdot2}=\dfrac{14}{20}\)
\(\dfrac{1}{4}=\dfrac{1\cdot5}{4\cdot5}=\dfrac{5}{20}\)
mà \(\dfrac{14}{20}>\dfrac{13}{20}>\dfrac{12}{20}>\dfrac{5}{20}\)
nên \(\dfrac{7}{10}>\dfrac{13}{20}>\dfrac{3}{5}>\dfrac{1}{4}\)
f: \(\dfrac{23}{28}=\dfrac{23\cdot1}{28\cdot1}=\dfrac{23}{28};\dfrac{9}{14}=\dfrac{9\cdot2}{14\cdot2}=\dfrac{18}{28}\)
\(\dfrac{3}{4}=\dfrac{3\cdot7}{4\cdot7}=\dfrac{21}{28};\dfrac{5}{7}=\dfrac{5\cdot4}{7\cdot4}=\dfrac{20}{28}\)
mà \(\dfrac{23}{28}>\dfrac{21}{28}>\dfrac{20}{28}>\dfrac{18}{28}\)
nên \(\dfrac{23}{28}>\dfrac{3}{4}>\dfrac{5}{7}>\dfrac{9}{14}\)
Bài 1 :
\(\dfrac{14}{7}>\dfrac{9}{7}\) \(\dfrac{6}{13}< 1\) \(\dfrac{7}{9}=\dfrac{14}{18}\) \(\dfrac{4}{9}< \dfrac{26}{45}\)
\(\dfrac{11}{24}>\dfrac{3}{8}\) \(\dfrac{42}{91}< \dfrac{7}{13}\) \(\dfrac{34}{64}< \dfrac{13}{16}\) \(\dfrac{17}{30}>\dfrac{8}{15}\)
bài 2
\(\dfrac{12}{17};\dfrac{2}{2};\dfrac{4}{7};\dfrac{9}{14}\) \(\dfrac{19}{15};\dfrac{13}{15};\dfrac{2}{3};\dfrac{2}{5}\) \(\dfrac{2}{3};\dfrac{11}{18};\dfrac{5}{9};\dfrac{1}{2}\)
\(\dfrac{5}{4};\dfrac{1}{2};\dfrac{7}{16};\dfrac{3}{8}\) \(\dfrac{7}{10};\dfrac{13}{20};\dfrac{7}{10};\dfrac{1}{4}\) \(\dfrac{23}{18};\dfrac{3}{4};\dfrac{5}{7};\dfrac{9}{14}\)
bài 3
những phân số thuộc " ? " là \(\dfrac{7}{8};\dfrac{1}{2};\dfrac{27}{24};\dfrac{26}{16}\)
bài 4
\(\dfrac{1}{4}=\dfrac{9}{36};\dfrac{2}{9}=\dfrac{8}{36}\)
\(\dfrac{5}{12}=\dfrac{15}{36};\dfrac{4}{36}\)
\(\Rightarrow\dfrac{15}{36}>\dfrac{9}{36}>\dfrac{8}{36}>\dfrac{4}{36}\)\(\Rightarrow\)ngọc là lớp trưởng
