2–68 Ideally, a voltmeter has infinite internal resistance and can be placed across any device to read the voltage without affecting the result. A particular digital multimeter (DMM), a common laboratory tool, is connected across the circuit shown in Figure P2−68. The expected voltage was 10.2 V. However, the DMM reads 7.61 V. The large, but finite, internal resistance of the DMM was “loading” the circuit and causing a wrong measurement to be made. Find the value of the internal resistance RM of this DMM.

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15 V 4.7 W DMM 10 RM +1 FIGURE P2-68