A 12V battery has an internal resistance of 0.5Ω and is connected to a 5.5Ω external resistor. An ammeter of resistance 0.1Ω is inserted in series to measure the current. By what approximate percentage does the current decrease due to the presence of the ammeter?
a) 3.0%
b) 16%
c) 1.6%
d) 1.8%