69. Вычислите: а) \(\frac47a:\frac{16}{23}\), \(a=7\); б) \(\frac35a:\frac67\), \(a=5\); в) \(\frac49a\cdot\frac1{11}\), \(a=11\); г) \(\frac{11}{15}a\cdot\frac{10}{11}\), \(a=2\); д) \(\frac{15}{17}a:\frac7{17}\), \(a=1\); е) \(\frac3{13}a:\frac5{13}\), \(a=4\); ж) \(\frac59\cdot\frac7{10}a\), \(a=3\); з) \(\frac13a:\frac49\), \(a=5\); и) \(\frac8{17}a\cdot\frac{51}{16}\), \(a=2\); к) \(\frac{51}{50}a:\frac{17}{100}\), \(a=10\); л) \(\frac7{11}\cdot\frac{121}{126}a\), \(a=5\); м) \(\frac5{12}a\cdot\frac35\), \(a=4\).

1. \(\frac47\cdot7:\frac{16}{23}=4\cdot\frac{23}{16}=\frac{23}{4}\).
2. \(\frac35\cdot5:\frac67=3\cdot\frac76=\frac72\).
3. \(\frac49\cdot11\cdot\frac1{11}=\frac49\).
4. \(\frac{11}{15}\cdot2\cdot\frac{10}{11}=\frac43\).
5. \(\frac{15}{17}\cdot1:\frac7{17}=\frac{15}{17}\cdot\frac{17}{7}=\frac{15}{7}\).
6. \(\frac3{13}\cdot4:\frac5{13}=\frac{12}{13}\cdot\frac{13}{5}=\frac{12}{5}\).
7. \(\frac59\cdot\frac7{10}\cdot3=\frac76\).
8. \(\frac13\cdot5:\frac49=\frac53\cdot\frac94=\frac{15}{4}\).
9. \(\frac8{17}\cdot2\cdot\frac{51}{16}=3\).
10. \(\frac{51}{50}\cdot10:\frac{17}{100}=\frac{51}{5}\cdot\frac{100}{17}=60\).
11. \(\frac7{11}\cdot\frac{121}{126}\cdot5=\frac{35}{18}\).
12. \(\frac5{12}\cdot4\cdot\frac35=1\).

Ответ: а) \(\frac{23}{4}\); б) \(\frac72\); в) \(\frac49\); г) \(\frac43\); д) \(\frac{15}{7}\); е) \(\frac{12}{5}\); ж) \(\frac76\); з) \(\frac{15}{4}\); и) \(3\); к) \(60\); л) \(\frac{35}{18}\); м) \(1\).