Three resistors of resistance 15 Ω each are to be connected in combination. The ratio of maximum equivalent resistance to the minimum equivalent resistance is:

9 : 1

The correct answer is Option (3) → 9 : 1

Three resistors each of $R = 15\ \Omega$

Maximum equivalent resistance occurs when all are in series:

$R_\text{max} = R + R + R = 3R = 45\ \Omega$

Minimum equivalent resistance occurs when all are in parallel:

$\frac{1}{R_\text{min}} = \frac{1}{R} + \frac{1}{R} + \frac{1}{R} = \frac{3}{R} \text{ implies } R_\text{min} = \frac{R}{3} = 5\ \Omega$

Ratio of maximum to minimum:

$\frac{R_\text{max}}{R_\text{min}} = \frac{45}{5} = 9$

Final Answer: 9