11) 3 2/3 + 1,4 = 3 2/3 + 1 6/15 = 3 2/3 + 1 2/5 = 3 10/15 + 1 6/15 = 4 16/15 = 5 1/15

Проверка: 1,4 = 1 2/5, а 2/3 = 10/15 и 2/5 = 6/15. Тогда 3 10/15 + 1 6/15 = 4 16/15 = 5 1/15.

Ответ: 5 1/15.