When resistors are connected in series, their resistances add up to give the total resistance of the combination. This can be calculated using the formula:
Total Resistance (R_total) = R1 + R2 + R3 + ... + Rn
Where:
R_total is the total resistance of the series combination.
R1, R2, R3, ... Rn are the resistances of each individual resistor in the series.
In words, you simply add up the resistance values of all the resistors connected in series to get the total resistance. Keep in mind that resistance is usually measured in ohms (Ω).