A series circuit is a circuit in which electrical components are connected in a single path, and share the same current.
To properly calculate the total resistance of a series circuit, find the resistance of each load applied to the circuit and add them together. The total resistance in this circuit would be the total of all three resistors plus the resistance of the wire. So the wire, 1 Ohm, plus the three resistors at 18 Ohms each = 55 Ohms.
These values were taken from these bulbs, each manufacturer could be different so just use these numbers for an example. A series circuit is one of the simplest electrical circuits to measure. Here's an example photo:
Series circuits depend on all the components working to operate the circuit. If one component fails, then all the ensuing components fail. Think of the old way that holiday lights were constructed, more specifically, if one bulb burnt out, the rest would not illuminate.