In which of the following kind of electric circuit the sum total of resistances decreases?
Parallel
In parallel connection the resistance of all elements is sum of reciprocal of individual resistances. Hence the total resistance of circuit decreases.Take an example we have two resistors in parallel of 2 and 3 ohm.
12 + 13 = 1R. Hence R = 65 =1.2 ohm which is less than individual resistance.