69. Вычислите: 1) \(\frac47a:\frac{16}{23},\ a=7\); 2) \(\frac35a:\frac67,\ a=5\); 3) \(\frac49a\cdot\frac1{11},\ a=11\); 4) \(\frac{11}{15}a\cdot\frac{10}{11},\ a=2\); 5) \(\frac{15}{17}a:\frac7{17},\ a=1\); 6) \(\frac3{13}a:\frac5{13},\ a=4\); 7) \(\frac59\cdot\frac7{10}a,\ a=3\); 8) \(\frac13a:\frac49,\ a=5\); 9) \(\frac8{17}a\cdot\frac{51}{16},\ a=2\); 10) \(\frac{51}{50}a:\frac{17}{100},\ a=10\); 11) \(\frac7{11}\cdot\frac{121}{126}a,\ a=5\); 12) \(\frac5{12}a\cdot\frac35,\ a=4\).

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: \(\frac{23}{4};\ \frac72;\ \frac49;\ \frac43;\ \frac{15}{7};\ \frac{12}{5};\ \frac76;\ \frac{15}{4};\ 3;\ 60;\ \frac{35}{18};\ 1\).