How to calculate voltage in an open resistor circuit
Without a voltmeter you would have

\$V_{cd} = V_{bd} = V_{ad} \approx 4.65 \mathrm{V}\$.

The reason is that with an open circuit, the current through each resistor is 0, and so by Ohm's law, the voltage drop across each resistor is 0.

The only reason you don't read this result with your meter is that there is a small leakage current through the voltmeter when you connect it to the circuit.