37. In a closed circuit consisting of a battery and a resistor with a resistance of 20 Ohms, a voltmeter was connected, first in series, then parallel to the resistor. The voltmeter readings are the same in both cases. The resistance of the voltmeter is 500 ohms. Determine the internal resistance of the battery.

Detailed solution. Decorated in Microsoft Word 2003. (Target decided to use formula editor)