I have to find the current flowing through the resistor connecting node a to d. I know it's a current divider problem, but I'm having a hard time finding the correct expression. I presume R5 is obsolete, since it's connected to an open circuit. Since \$R_{1}\$, \$R_{2}\$, \$R_{4}\$ are connected in parallel, their equivalent resistance \$\frac{1}{R_{T}} = \frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{1}{R_{4}} \$. Since we have to find the current through through \$R_{3}\$, the current \$i\$ should be:
$$ i = I_{0} \frac{R_{T}}{R_{3}+R_{T}} $$.
Is this correct? Am I doing something wrong?