計算：
(1)$(-85)×(-25)×(-4)$； (2)$(-125)×(-25)×4×0×(-8)$；
(3)$(\frac {7}{9}-\frac {5}{6}+\frac {3}{4}-\frac {7}{18})×36$； (4)$(\frac {1}{6}-\frac {3}{4}+\frac {1}{12})×(-48)$；
(5)$(-5)×(-7)+5×(-6)$； (6)$4×(-3\frac {6}{7})-3×(-3\frac {6}{7})-6×3\frac {6}{7}$；
(7)$99\frac {24}{25}×(-25)$； (8)$(-1\frac {5}{17})×(-3\frac {1}{8})×(+\frac {8}{15})×(+3\frac {7}{9})$；
(9)$(1+\frac {1}{2})×(1+\frac {1}{4})×(1+\frac {1}{6})×... ×(1+\frac {1}{20})×(1-\frac {1}{3})×(1-\frac {1}{5})×(1-\frac {1}{7})×... ×(1-\frac {1}{21})$.
答案：(1)-8500 (2)0 (3)11 (4)24 (5)5 (6)-27 (7)-2499 (8)$\frac{220}{27}$ (9)解：$(1+\frac{1}{2})×(1+\frac{1}{4})×(1+\frac{1}{6})×\dots×(1+\frac{1}{20})×(1-\frac{1}{3})×(1-\frac{1}{5})×(1-\frac{1}{7})×\dots×(1-\frac{1}{21})$
$=\frac{3}{2}×\frac{5}{4}×\frac{7}{6}×\dots×\frac{21}{20}×\frac{2}{3}×\frac{4}{5}×\frac{6}{7}×\dots×\frac{20}{21}$
$=(\frac{3}{2}×\frac{2}{3})×(\frac{5}{4}×\frac{4}{5})×(\frac{7}{6}×\frac{6}{7})×\dots×(\frac{21}{20}×\frac{20}{21})$
$=1×1×1×\dots×1=1.$
