CAIE IGCSE Physics 4.3.2.10 Combined Resistance of Two Resistors Questions

Fig. 7.1 shows a circuit that contains a battery, a switch, a voltmeter and three $40 \Omega$ resistors, $\mathrm{R}_{1}$, $R_{2}$ and $R_{3}$.

The switch is open and resistors $R_{1}$ and $R_{2}$ form a potential divider.

The reading on the voltmeter is 7.5 V .

The switch is closed.

Calculate the resistance of the complete circuit.