An ammeter and a voltmeter are joined in series to a cell. Their readings are A and V respectively. A resistance is now joined in parallel with the voltmeter. Then,

Since a resistor is joined in parallel to the voltmeter, the resistance of voltmeter and resistor combination is lesser than that of only voltmeter earlier. Hence the voltage across the voltmeter reduces and that across ammeter increases. Hence V decreases. Also since the total resistance of the circuit is also decreased, the current through the ammeter increases. Hence A increases.