1)

[tex]6 \frac{7}{8} - 3 \frac{1}{3} + 5 \frac{5}{16} = 6 \frac{42}{48} - 3 \frac{16}{48} + 5 \frac{15}{48} = \\ 11 \frac{57}{48} - 3 \frac{16}{48} = 8 \frac{41}{48} [/tex]

2)

[tex]5 \frac{9}{14} - 2 \frac{3}{7} + 6.7 = 5 \frac{9}{14} - 2 \frac{6}{14} + 6 \frac{7}{10} = \\ = 3 \frac{3}{14} + 6 \frac{7}{10} = 3 \frac{15}{70} + 6 \frac{49}{70} = 9 \frac{64}{70} = 9 \frac{32}{35} [/tex]

3)

[tex](15 \frac{5}{6} - 9 \frac{25}{27} ) - 2 \frac{17}{18} = 15 \frac{45}{54} - 9 \frac{50}{54} - 2 \frac{51}{54} = \\ = 15 \frac{45}{54} - 11 \frac{101}{54} = 14 \frac{99}{54} - 12 \frac{47}{54} = 2 \frac{52}{54} = 2 \frac{26}{27} [/tex]

4)

[tex](18 - 10 \frac{5}{9} ) - (6 \frac{1}{8} - 3 \frac{2}{3} ) = 18 - 10 \frac{5}{9} - 6 \frac{1}{8} + 3 \frac{2}{3} = \\ = 18 - 10 \frac{40}{72} - 6 \frac{9}{72} + 3 \frac{48}{72} = 21 \frac{48}{72} - 16 \frac{49}{72} = \\ = 20 \frac{120}{72} - 16 \frac{49}{72} = 4 \frac{71}{72} [/tex]