what is the equivalent resistance for a series circuit with three resistors

In a series circuit the voltage drop across the resistors is different for each resistor while the current the current the flow through them is uniform.

Therefore  overall voltage is given by sum of the individual voltages the equivalent resistance is the sum of the individual resistance

From V=IR

V_EFF= V₁+V₂+V₃

IR_EFF=IR₁+ IR₂+ IR₃

_{the equivalent resistance is the sum of the individual resistance}