Дам 50 балов! 1,2,3,4,5 решить

1)
$\frac{7}{21}= \frac{1}{3} \\ \\ \frac{20}{35}= \frac{4}{7} \\ \\ \frac{48}{72}= \frac{2}{3}$

2)
\frac{11}{14} \\ \\ \frac{2}{3}> \frac{5}{8} " alt=" \frac{4}{9}< \frac{5}{9} \\ \\ \frac{6}{7}> \frac{11}{14} \\ \\ \frac{2}{3}> \frac{5}{8} " align="absmiddle" class="latex-formula">

3)
$a) \frac{5}{6}- \frac{7}{18}= \frac{15-7}{18}= \frac{8}{18}= \frac{4}{9} \\ \\ b) \frac{1}{4}+ \frac{2}{9}= \frac{9+8}{36}= \frac{17}{36} \\ \\ c) \frac{2}{21} + \frac{9}{14}= \frac{4+27}{42} = \frac{31}{42}$

4)
$1) \frac{5}{12}- \frac{1}{8}= \frac{10-3}{24}= \frac{7}{24}$ - тетрадей продали во второй день

$2) \frac{5}{12}+ \frac{7}{24}= \frac{10+7}{24} = \frac{17}{24}$ - тетрадей продали за два дня

5)
$x- \frac{2}{5}= \frac{3}{7} - \frac{8}{35} \\ \\ x=\frac{3}{7} - \frac{8}{35}+ \frac{2}{5} \\ \\ x= \frac{15-8+14}{35} \\ \\ x= \frac{21}{35} = \frac{3}{5}$