Выполни сложение дробей:

3/7+1/9; 3/10+1/8; 7/12+4/15; 3/4+5/6; 2/5+3/7; 9/14++2/21; 2/3+2/151/12+5/9; 3/20+6/25; 1/3+5/8; 1/6+2/9; 7/9+2/15

Приводим дроби в общему знаменателю (в скобках добавочный множитель к дроби)

3/7 (9) + 1/9 (7) = 27/72+7/72=34/72=17/36;

3/10 (8) + 1/8 (10) = 24/80+10/80=34/80=17=40;

7/12 (5) + 4/15 (4) = 35/60+16/60=51/60;

3/4 (3) + 5/6 (2) = 9/12+10/12=19/12=1, 7/12

2/5 (7) + 3/7 (5) = 14/35+15/35=29/35

9/14 (3) + 2/21 (2) = 27/42+4/42=31/42

2/3+2/1 (3) = 2/3+6/3=8/3=2,2/3

51/12 (3) + 5/9 (4) = 153/36+20/36=173/36=4,29/36

3/20 (5) + 6/25 (4) = 15/100+24/100=0,39

1/3 (8) + 5/8 (3) = 8/24+15/24=13/24

1/6 (6) + 2/9 (4) = 6/36+8/36=14/36=7/18

7/9 (5) + 2/15 (3) = 35/45+6/45=41/45