The ammeter reads 2 amps.
A 1 ohm resistor* is half as resistant as a 2 ohm resistor,
so it is twice as easy for the current* to flow.
The resistor allows twice the 1 amp current to pass.
By Ohm's Law:
V = IR
Solving for I:
Now replacing the symbols with the values given:
2 = I
I = 2 amps