计算:
(1)$10-(-6)+8-(+2)$; (2)$-17+(-6)+23-(-20)$;
(3)$4.7-(-8.9)-7.5+(-6)$; (4)$-72+(-32)+(-8)+72$;
(5)$-7+(-33)-10-(-16)$; (6)$12-(-18)+(-7)-20$;
(7)$2\frac {2}{3}+6.3-(\frac {5}{3}-1\frac {3}{5})$; (8)$\frac {5}{6}+(-\frac {3}{4})-(+0.25)-(-\frac {1}{6})$;
(9)$1-3+5-7+9-11+... +97-99$.
(1)$10-(-6)+8-(+2)$; (2)$-17+(-6)+23-(-20)$;
(3)$4.7-(-8.9)-7.5+(-6)$; (4)$-72+(-32)+(-8)+72$;
(5)$-7+(-33)-10-(-16)$; (6)$12-(-18)+(-7)-20$;
(7)$2\frac {2}{3}+6.3-(\frac {5}{3}-1\frac {3}{5})$; (8)$\frac {5}{6}+(-\frac {3}{4})-(+0.25)-(-\frac {1}{6})$;
(9)$1-3+5-7+9-11+... +97-99$.
答案：(1)22 (2)20 (3)0.1 (4)-40 (5)-34 (6)3 (7)8.9 (8)0 (9)-50
解析：
(1)解：10 - (-6) + 8 - (+2)
= 10 + 6 + 8 - 2
= 16 + 8 - 2
= 24 - 2
= 22
(2)解：-17 + (-6) + 23 - (-20)
= -17 - 6 + 23 + 20
= -23 + 23 + 20
= 0 + 20
= 20
(3)解：4.7 - (-8.9) - 7.5 + (-6)
= 4.7 + 8.9 - 7.5 - 6
= 13.6 - 7.5 - 6
= 6.1 - 6
= 0.1
(4)解：-72 + (-32) + (-8) + 72
= (-72 + 72) + (-32 - 8)
= 0 + (-40)
= -40
(5)解：-7 + (-33) - 10 - (-16)
= -7 - 33 - 10 + 16
= -40 - 10 + 16
= -50 + 16
= -34
(6)解：12 - (-18) + (-7) - 20
= 12 + 18 - 7 - 20
= 30 - 7 - 20
= 23 - 20
= 3
(7)解：$2\frac{2}{3} + 6.3 - (\frac{5}{3} - 1\frac{3}{5})$
$= \frac{8}{3} + 6.3 - \frac{5}{3} + 1.6$
$= (\frac{8}{3} - \frac{5}{3}) + (6.3 + 1.6)$
= 1 + 7.9
= 8.9
(8)解：$\frac{5}{6} + (-\frac{3}{4}) - (+0.25) - (-\frac{1}{6})$
$= \frac{5}{6} - \frac{3}{4} - \frac{1}{4} + \frac{1}{6}$
$= (\frac{5}{6} + \frac{1}{6}) - (\frac{3}{4} + \frac{1}{4})$
= 1 - 1
= 0
(9)解：1 - 3 + 5 - 7 + 9 - 11 +... + 97 - 99
= (1 - 3) + (5 - 7) + (9 - 11) +... + (97 - 99)
= (-2) + (-2) + (-2) +... + (-2)（共25个-2）
= -2×25
= -50
= 10 + 6 + 8 - 2
= 16 + 8 - 2
= 24 - 2
= 22
(2)解：-17 + (-6) + 23 - (-20)
= -17 - 6 + 23 + 20
= -23 + 23 + 20
= 0 + 20
= 20
(3)解：4.7 - (-8.9) - 7.5 + (-6)
= 4.7 + 8.9 - 7.5 - 6
= 13.6 - 7.5 - 6
= 6.1 - 6
= 0.1
(4)解：-72 + (-32) + (-8) + 72
= (-72 + 72) + (-32 - 8)
= 0 + (-40)
= -40
(5)解：-7 + (-33) - 10 - (-16)
= -7 - 33 - 10 + 16
= -40 - 10 + 16
= -50 + 16
= -34
(6)解：12 - (-18) + (-7) - 20
= 12 + 18 - 7 - 20
= 30 - 7 - 20
= 23 - 20
= 3
(7)解：$2\frac{2}{3} + 6.3 - (\frac{5}{3} - 1\frac{3}{5})$
$= \frac{8}{3} + 6.3 - \frac{5}{3} + 1.6$
$= (\frac{8}{3} - \frac{5}{3}) + (6.3 + 1.6)$
= 1 + 7.9
= 8.9
(8)解：$\frac{5}{6} + (-\frac{3}{4}) - (+0.25) - (-\frac{1}{6})$
$= \frac{5}{6} - \frac{3}{4} - \frac{1}{4} + \frac{1}{6}$
$= (\frac{5}{6} + \frac{1}{6}) - (\frac{3}{4} + \frac{1}{4})$
= 1 - 1
= 0
(9)解：1 - 3 + 5 - 7 + 9 - 11 +... + 97 - 99
= (1 - 3) + (5 - 7) + (9 - 11) +... + (97 - 99)
= (-2) + (-2) + (-2) +... + (-2)（共25个-2）
= -2×25
= -50