Answer :
The resistance of R2 is 0.06 kilo-ohms, found by solving the parallel resistance formula when R1 = 20 ohms and RT = 15 ohms. Hence, b is the correct option.
The student is asking about the resistance of a resistor labeled R2 when given the resistance of another resistor R1 and the total resistance RT of the circuit. Since the total resistance (RT) is less than the resistance of R1, we can deduce that the two resistors are connected in parallel. The total resistance in a parallel circuit is given by the formula:
1/RT = 1/R1 + 1/R2
Plugging in the given values:
1/15 Ω = 1/20 Ω + 1/R2
Solving for R2 yields:
1/R2 = 1/15 - 1/20
1/R2 = (4 - 3)/60
1/R2 = 1/60
R2 = 60 Ω
Since the student asked the result in kilo-ohms:
R2 = 60 Ω / 1000 = 0.06 kilo-Ω
Therefore, the resistance of R2 is 0.06 kilo-ohms, which corresponds to option b.
