10 баллов номер 1091

1091.
1)
5/6 * 9/15 - 5/12 * 4/15 =
$\frac{5}{2*3}* \frac{3*3}{3*5} - \frac{5}{3*4}* \frac{4}{3*5}= \frac{1}{2}- \frac{1}{9}= \frac{7}{18}$
2)
$\frac{7}{2*9}* \frac{9}{2*7}+ \frac{1}{3}* \frac{2*3}{7}= \frac{1}{4}+ \frac{2}{7}= \frac{15}{28}$
3)
$\frac{3*3*2}{5*4*3}+ \frac{5*7}{2*7*5*5}= \frac{6}{10}+ \frac{1}{10}= \frac{7}{10}$
4)
$\frac{15*2}{4*5}- \frac{81*5}{27*25}= \frac{3}{2}- \frac{3}{5}= \frac{9}{10}$