Answer
Formula
Resistance for parallel circuit.
\(\frac{1}{R_{Total}} = \frac{1}{R_{1}} +\frac{1}{R_{2}}\)
As given
A circuit contains two devices that are connected in parallel.
if the resistance of one of these devices is 12 ohms and the resistance of the other device is 4 ohms.
\(R_{1} = 12\ ohms\)
\(R_{2} = 4\ ohms\)
Put in the above
\(\frac{1}{R_{Total}} = \frac{1}{R_{1}}+\frac{1}{R_{2}}\)
\(\frac{1}{R_{Total}} = \frac{1}{12}+\frac{1}{4}\)
L.C.M of (12,4)= 12
\(\frac{1}{R_{Total}} = \frac{1 + 3}{12}\)
\(\frac{1}{R_{Total}} = \frac{4}{12}\)
\(R_{Total} = \frac{12}{4}\)
\(R_{Total} = 3\ ohms\)
Therefore the total resistance of the two devices is 3 ohms .
Option (b) is correct .
