分数加减混合运算

0，1，20/21，

1-3/8-5/8
=1-(3/8+5/8)
=1-1
=0
2/3+7/9-4/9

=6/9+7/9-4/9
=9/9
=1
6/7-(1/3-2/7)
=6/7+2/7-1/3
=8/7-1/3
=17/21
x+4/15=2/3
x=2/3-4/15
x=2/5
x+7/12=2/3+3/4
x+7/12=17/12
x=17/12-7/12
x=5/6
x-3/8+1/4=1/2
x-1/8=1/2
x=1/2+1/8
x=5/8

1-1/4-3/4
5/7+5/9+2/7+4/9
4/6+2/6-2/5-3/5
1/2+3/4+5/8
3/10+4/5+7/20
3/8+2/3-5/6
4/5-(1/3+3/10)
11-4/15-11/15
16-(14/19+9/25)
1-(1/5+1/7)
1/4+1/8+1/6-1/24
3/4-1/2+2/3
1/6+2/5+7/10
2/3-1/4-1/5
19/20-(1/4+2/5)
7/8-(7/10-11/20)
15/16+4/5-15/16
3/5-1/4+3/5
4/15+9/20-3/10
18/20-(1/4+2/5)
5/8+7/12-4/9
17/18-(1/12+1/6)
1/2+1/4-1/8
(14/15-2/5)-1/3
4/11+2/5+7/11+1/5
4/5-3/10+2/3
3/7-(9/14-1/2)
8/9-5/9+1/6

你是五年级的吗？什么小学？