Open Circuit Voltage, Thevenin Equivalent

Homework Statement

Find the open circuit voltage across A & B:

V = IR

The Attempt at a Solution

If I0 is the current leaving the voltage source and passing through the first resistor, I1 is the current through the left resistor in parallel, and I2 through the two other resistors, then:

$$V - I_0 R - I_1 R = 0$$

$$-2 I_2 R + I_1 R = 0$$

$$I_0 = I_1 + I_2$$

Solving gives a current $$I_2 = \frac{2 V}{5R}$$, therefore the potential difference across the A & B terminals is $$\Delta V = I_2 R = \frac{2 V}{5}$$

The book says this is [tex]\frac{V}{5}[tex].

Am I doing something wrong, or have I found an error in the book?