Решение:
1. $2 - 1\frac{13}{28} = 2 - \frac{41}{28} = \frac{56}{28} - \frac{41}{28} = \frac{15}{28}$
2. $\frac{15}{28} : \frac{25}{49} = \frac{15}{28} * \frac{49}{25} = \frac{3*5}{4*7} * \frac{7*7}{5*5} = \frac{3*7}{4*5} = \frac{21}{20}$
3. $\frac{8}{15} + \frac{21}{20} = \frac{8*4}{15*4} + \frac{21*3}{20*3} = \frac{32}{60} + \frac{63}{60} = \frac{95}{60} = \frac{19}{12}$
4. $1\frac{1}{4} = \frac{5}{4}$
5. $\frac{19}{12} - \frac{5}{4} = \frac{19}{12} - \frac{5*3}{4*3} = \frac{19}{12} - \frac{15}{12} = \frac{4}{12} = \frac{1}{3}$
Ответ: $\frac{1}{3}$