Two 20 Ohm conductors are connected in series. The total resistance of the conductors is …

We have two guides. Each has a resistance of 20 ohms.

This means that each conductor creates resistance for the passage of current inside itself.

Now let’s imagine that the current must simultaneously pass through two conductors, where each will slow down the passage of the current.

Accordingly, both conductors will resist the passage of current. From this it follows that it is necessary to add the resistances of all series-connected conductors.

Solution 20 + 20 = 40 OM.