No matter how many resistors in series there are, two or ten, just specify the number of resistors and the resistance value for each one.
\(R_t = R_1 + R_2 + R_3 + ... + R_n \)
\(R_t\) = total resistance
\(R_2\) = resistance of second resistor
\(R_3\) = resistance of third resistor
\(R_n\) = resistance of number resistor