1) (7/15 - 1/6) + 2/5 = 7/10
1. 7/15 - 1/6 = 7/15 - 1/6 = 7·2/15·2 - 1·5/6·5 = 14/30 - 5/30 = 14 - 5/30 = 9/30 = 3·3/10·3 = 310
2. 3/10 + 2/5 = 3/10 + 4/10 =7/10
2) (3/8 - 1/9) + 25/36 = 23/24
1. 3/8 - 1/9 = 27/ 72 - 8/72 = 19 / 72
2. 19/72 + 25/36 =19 / 72 + 50 /72 = 69/72 = 23/24
3) ( 8/9 - 5/6) + 2/3 = 13/18
1. 8/9 - 5/6 = 16 /18 - 15/18 = 1/18
2. 1/18 + 2/3 = 1/18 + 12 /18 = 13/18
4) ( 7/8 - 13/20 ) + 9/10 =
1. 7/8 - 13/20 = 35/ 40 - 26/40 = 9/40
2. 9/40 + 9/10 = 9/40 + 36 /40 = 45/40 = 9/8 = 1 целая 1/8