Решите 2 уравнения: (2/3x-2/5) * 15=8.2/3 х+7/3 х=18. Найдите значение выражения: 21/25*5/7-3/16*4/155 целых5/12*4/13-2 целых5/8*3/14

1) (2/3 х - 2/5) * 15 = 8;

2/3 х * 15 - 2/5 * 15 = 8;

2 * 5 х - 2 * 3 = 8;

10 х - 6 = 8;

10 х = 8 + 6;

10 х = 14;

х = 14 : 10;

х = 1,4.

2) 2/3 х + 7/3 х = 18;

(2 + 7) / 3 х = 18;

9/3 х = 18;

3 х = 18;

х = 18 : 3;

х = 6.

3) 21/25 * 5/7 - 3/16 * 4/15 = (7 * 3 * 5) / (5 * 5 * 7) - (3 * 4) / (4 * 4 * 3 * 5) = 3/5 - 1/20 = 12/20 - 1/20 = 11/20;

4) 5 5/12 * 4/13 - 2 5/8 * 3/14 = (5 * 12 + 5) / 12 * 4/13 - (2 * 8 + 5) / 8 * 3/14 = (60 + 5) / 12 * 4/13 - (16 + 5) / 8 * 3/14 = 65/12 * 4/13 - 21/8 * 3/14 = (13 * 5 * 4) / (4 * 3 * 13) - (7 * 3 * 3) / (8 * 2 * 7) = 5/3 - 9/16 = 80/48 - 27/48 = 53/48 = 1 5/48.