What is the equivalent resistance between points A and B?
We can see that the resistors 20 ohm, 20 ohm, and 20 ohm are connected in series (see figure below). We replace these resistors by an equivalent resistor with the resistance of
Then we get the circuit shown in the figure below.
In this circuit two resistors 10 ohm and 10 ohm are connected in series. We can replace them with an equivalent resistor with the resistance of (see figure below)
Finally, we have three resistors (60 ohm, 20 ohm, and 30 ohm) connected in parallel (see figure below). The equivalent resistance of these resistors can found from the following expression
Then the equivalent resistance of the circuit is 10 ohm.