Resistors in parallel are typically connected in parallel between two nodes, for example, between node b and e in the figure above, one end of all three resistors are connected to node b and all other ends connected to node e. Their equivalent resistance R is :

Add more resistors in parallel will decrease the resistance R in combination. The potential drop V across each resistor in a parallel combination is the same. The total current is equal to the sum of all parallel branch currents.

For resistors in series as below:

Their equivalent resistance R is:

Add more resistors in series will increase the resistance R in combination. The total potential drop V across the combination is equal to the sum of each resistance potential drops. The current through each resistance is the same.