298. Эсептегиле: a) 7/15 - 3/5; b) 5/7 + 9/77; c) 1/32 - 29/40; d) 5/42 - 8/24 + 1/8; e) 9/13 - 5/26 + 4/9; f) 7/9 : 5 + 4/5 * 7/8.

Решим примеры:

1. $$ \frac{7}{15} - \frac{3}{5} = \frac{7}{15} - \frac{3 \cdot 3}{5 \cdot 3} = \frac{7}{15} - \frac{9}{15} = \frac{7-9}{15} = \frac{-2}{15} = -\frac{2}{15}.$$
   Ответ: $$-\frac{2}{15}$$
2. $$\frac{5}{7} + \frac{9}{77} = \frac{5 \cdot 11}{7 \cdot 11} + \frac{9}{77} = \frac{55}{77} + \frac{9}{77} = \frac{55+9}{77} = \frac{64}{77}.$$
   Ответ: $$\frac{64}{77}$$
3. $$-\frac{1}{32} - \frac{29}{40} = -\frac{1 \cdot 5}{32 \cdot 5} - \frac{29 \cdot 4}{40 \cdot 4} = -\frac{5}{160} - \frac{116}{160} = \frac{-5-116}{160} = \frac{-121}{160} = -\frac{121}{160}.$$
   Ответ: $$-\frac{121}{160}$$
4. $$\frac{5}{42} - \frac{8}{24} + \frac{1}{8} = \frac{5}{42} - \frac{1}{3} + \frac{1}{8} = \frac{5 \cdot 4}{42 \cdot 4} - \frac{1 \cdot 56}{3 \cdot 56} + \frac{1 \cdot 21}{8 \cdot 21} = \frac{20}{168} - \frac{56}{168} + \frac{21}{168} = \frac{20-56+21}{168} = \frac{-15}{168} = -\frac{5}{56}.$$
   Ответ: $$-\frac{5}{56}$$
5. $$\frac{9}{13} - \frac{5}{26} + \frac{4}{9} = \frac{9 \cdot 18}{13 \cdot 18} - \frac{5 \cdot 9}{26 \cdot 9} + \frac{4 \cdot 26}{9 \cdot 26} = \frac{162}{234} - \frac{45}{234} + \frac{104}{234} = \frac{162 - 45 + 104}{234} = \frac{221}{234}.$$
   Ответ: $$\frac{221}{234}$$
6. $$\frac{7}{9} : 5 + \frac{4}{5} \cdot \frac{7}{8} = \frac{7}{9} : \frac{5}{1} + \frac{4}{5} \cdot \frac{7}{8} = \frac{7}{9} \cdot \frac{1}{5} + \frac{1}{5} \cdot \frac{7}{2} = \frac{7}{45} + \frac{7}{10} = \frac{7 \cdot 2}{45 \cdot 2} + \frac{7 \cdot 9}{10 \cdot 9} = \frac{14}{90} + \frac{63}{90} = \frac{14+63}{90} = \frac{77}{90}.$$
   Ответ: $$\frac{77}{90}$$