用简便方法计算.
5346-1999
解,得：
==5346-（2000-1）
==5346-2000+1
==3346+1
==3347
38.75-15.38+61.25-4.62
解,得：
==（38.75+61.25）-（15.38+4.62）
==100-20
==80
(1/2)+(1/6)+(1/12)+(1/20)+(1/30)
解,得：
==[1-(1/2)]+[(1/2)-(1/3)]+[(1/3)-(1/4)]+[(1/4)-(1/5)]+[(1/5)-(1/6)]
==1-(1/6)
==5/6
(172/13)-2.25-(31/4)
解,得：
==(172/13)-[(9/4)+(31/4)]
==(172/13)-10
==(172-130)/13
==42/13
(21/2)-(0.33+0.5)
解,得：
==10.5-0.33-0.5
==10.5-0.5-0.33
==10-0.33
==9.67