2、 1/5- 1/7=2/35。

3、 1/4+ 1/9= 13/36。

4、 1/4- 1/9=5/36。

5、 1/8+ 1/9= 17/72。

6、 1/8- 1/9= 1/72。

7、 1/ 10+7/9=79/90。

8、5/7- 1/6=23/42。

9、 1-5/9=4/9。

10、 1/5+3/8=23/40。

12、3/4+ 1/5= 19/20。

13、2/3-3/5= 1/5。

14、 1-2/5=3/5。

15、5/8- 1/9=37/72。

16、 1/0- 1/20= 1/20。

17、 1/6+3/8= 13/24。

18、5/9- 1/2= 1/ 18。

19、2/3+ 1/4= 1 1/ 12。

20、 1/2+ 1/3=5/6。

Extended data:

The addition and subtraction of fractions are:

1, add and subtract fractions with the same denominator, only add and subtract numerators, and the denominator remains unchanged;

2. Add and subtract scores of different denominators. Divide into fractions with the same denominator first, and then add and subtract fractions with the same denominator. After adding and subtracting scores, if the scores obtained are not reduced scores, they should be reduced and divided into reduced scores.

Baidu Encyclopedia-Fraction Addition and Subtraction Rule