Дроби вычислите:а) 5 /8 + 3 /16;б) 3целая 2/9:2целая5/12;в) 1целая-2/9×3/8;

Первый пример.

5/8 + 3/16 = 13 /16;

5/8 + 3/16 = 5 * 16/8 * 16 + 3 * 8/16 * 8 = 80/128 + 24/128 = 80 + 24/128 = 104/128 = 13 * 8/16 * 8 = 13/16.

Второй пример.

3 2/9 / 2 5/12 = 1 1/3;

3 2/9 / 2 5/12 = 3 * 9 + 2/9 / 2 *12 + 5/12 = 29/9 / 29/12 = 29/9 * 12/29 = 29 * 12/9 * 29 = 348/261 = 4 * 87/3 * 87 = 4/3 = 1 + 1 * 3/3 = 1 1/3.

Третий пример.

1 - 2/9 * 3/8 = 11/12;

Первое действие.

2/9 * 3/8 = 2 * 3/9 * 8 = 6/72 = 1 * 6/12 * 6 = 1/12;

Второе действие.

1/1 - 1/12 = 1 * 12/1 * 12 - 1 * 1/12 * 1 = 12/12 - 1/12 = 12 - 1/12 = 11/12.