Equivalent resistance between A and B = series combination of 1 Ω and 2 Ω in parallel with 3 Ω resistor..
1
R
=
1
3
+
1
3
=
2
3
or R = 1.5 Ω ∴ Current in the circuit is I = V/R = 1.5/1.5 = 1A. Since the resistance in arm ACB = resistance in arm AB = 3 Ω, the current divides equally in the two arms. Hence the current through the 3 Ω resistor = 1/2 = 0.5 A.