Решение:
a) $$14\frac{9}{13} - 1\frac{5}{13} + 12\frac{11}{13} = 13\frac{4}{13} + 12\frac{11}{13} = 25\frac{15}{13} = 26\frac{2}{13}$$
б) $$7\frac{24}{25} - 3\frac{12}{25} - 1\frac{7}{25} = 4\frac{12}{25} - 1\frac{7}{25} = 3\frac{5}{25} = 3\frac{1}{5}$$
в) $$17\frac{7}{40} + 3\frac{9}{40} - \frac{17}{40} = 20\frac{16}{40} - \frac{17}{40} = 19\frac{56}{40} - \frac{17}{40} = 19\frac{39}{40}$$
г) $$23\frac{15}{49} - 13\frac{19}{49} - \frac{30}{49} = 9\frac{45}{49} - \frac{30}{49} = 9\frac{15}{49}$$
Ответ: а) 26\frac{2}{13}; б) 3\frac{1}{5}; в) 19\frac{39}{40}; г) 9\frac{15}{49}