The problems (Don't click until you start timing)

1. Problem 1. (30 pts)

   Find the equivalent resistance $R_{ab}$ between points a and b. (The diagonal wires are not connected to each other at the crossings.)

   

2. Problem 2. (30 points)

   Find voltage $V$ and current $I$ as labeled in the following figure:

   

   where $R_1=5\Omega$, $R_2=1\Omega$, $R_3=6\Omega$, $R_4=6\Omega$.

3. Problem 3. (40 pts)

   Find all six currents labeled as $I_1$ through $I_6$ in the figure, where $R1=4\Omega$, $R2=4\Omega$, $R3=2\Omega$, and $R4=2\Omega$.