Step-by-step explanation:
Resistors in circuits can either be connected in series or in parallel.
For a series connected resistors, the same current flows through the resistors while different voltages is passed across them. The formula for calculating effective resistances in a circuit is expressed as
where R1, R2, R3 etc. are the resistances connected in series.
The effective resistances for series connected resistors is the sum of the individual resistors
For a parallel connected resistors, different current flows through the resistors while same voltage is passed across them. The formula for calculating effective resistances in a circuit is expressed as:

The effective resistances for parallel connected resistors is the sum of the reciprocal of the individual resistors