Решить дроби; 2 7/10+ 9 2/15; 19 5/18+ 6 1/12; 15 1/21 + 8 1/28.

2 7/10+ 9 2/15; = 27/10 + 137/15 = (27*3+137*2)/30 = 355/30 = 11 25/30 = 11 5/6

19 5/18+ 6 1/12 = 347/18 + 73/12 = ( 347*2 + 73 *3)/36 = (694+219)/36 =913/36= 25 13/36

15 1/21 + 8 1/28 = 316/21 + 225/28 = (316*4+225*3)/84 = (1264 + 675)/84 = 1939 / 84= 23 7/84 = 23 1/12

2 7/10 + 9 2/15 = 27/10+ 137/15 = 162 /60 +548/60 =710/60 = 11 50/60 = 11 5/6
19 5/18 + 6 1/12 = 347/18 + 73/12 = 694/36 + 219/36 = 913 /36 = 25 13/36
15 1/21 + 8 1/28 = 316/21 + 225/28 = 8848/588 + 4725/588= 13573/588 =  23 49/588 = 23 1/12