Найдите значение выражения: а) 5/11 + 3/11 + 7/11; б) 9 13/19 + (8 18/19 - 3 15/19); в) 10 4/21 - (4 10/21 + 3 19/21).

а) (5+3+7)/11 = 15/11 = 1 4/11
б) 9 13/19 + (8+18-3-15)/19 = 9 13/19 + (26-18)/19 = 9 13/19 + 8/19 = 9 21/19 = 10 2/19
в) 10 4/21 - (4+3 + 10+19)/21 = 10 4/21 - (7 + 29/21) = 10 4/21 - (7 + 1 8/21) = 10 4/21 - 8 8/21 = 1 17/21