Question

用简便方法计算. 5346减1999 38.75-15.38+61.25-4.62

2分之1+6分之1+12分之1+20分之1+30分之1
13分之172-2.25-4分之31
2分之21-(0.33+0.5)
谢啦!

Answer 1

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

Answer 2

5346减1999
=5346-（2000-1）
=5346-2000+1
=3347;
38.75-15.38+61.25-4.62
=(38.75+61.25)-(15.38+4.62)
=100-20
=80;
2分之1+6分之1+12分之1+20分之1+30分之1
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6
=1-1/6
=5/6;
13分之172-2.25-4分之31
=172/13-(9/4+31/4)
=172/13-10
=172/13-130/13
=42/13
2分之21-(0.33+0.5)
=(21/2-0.5)-0.33
=10-0.33
=9.67

Answer 3

❶5346-1999+38.75-15.38+61.25-4.62
＝（5346+38.75+61.25）-（1999+15.38+4.62）
＝5446-2019
=3427