а) 3/5 + 3/7 + 9/7 × 4/15
решаем по действиям:
1) 9/7 × 4/15 = 36/105 = 12/35;
2) 3/5 + 3/7 = 21/35 + 15/35 = 36/35 = 1 1/35;
3) 1 1/35 + 12/35 = 1 + 1/35 + 12/35 = 1 + 13/35 = 1 13/35;
Ответ : 1 13/35.
в) 7/8 + 5/8 × 1/3 + 2/3
решаем по действиям:
1) 5/8 × 1/3 = 5/24;
2) 7/8 + 5/24 = 21/24 + 5/24 = 26/24 = 13/12 = 1 1/12;
3) 1 1/12 + 2/3 = 1 + 1/12 + 2/3 = 1 + 1/12 + 8/12 = 1 + 9/12 = 1 + 3/4 = 1 3/4;
Ответ : 1 3/4