Ответ:

а) Проверим варианты: \(\frac{12}{73}\approx0.164\), \(\frac{43}{92}\approx0.467\), \(\frac{13}{43}\approx0.302\), \(\frac{48}{83}\approx0.578\). Только \(0.4<\frac{43}{92}<0.5\).

б) \(\frac{19}{54}\approx0.352\), \(\frac{18}{37}\approx0.486\), \(\frac{17}{23}\approx0.739\), \(\frac{16}{25}=0.64\). Только \(0.6<\frac{16}{25}<0.7\).

Ответ: а) 2) \(\frac{43}{92}\); б) 4) \(\frac{16}{25}\).