posted by Bee .
why does current slow down in a series than when in a parallel?
It does not SLOW down. The magnitude of the current is lower, say 4 amps from original 8 amps, but that is not slower.
Speed of current is measured in terms of velocity, meter/second, and the magnitude of current is measured in amperes.
In a series circuit, more resistance is offered than in a parallel path. By defintion, resistance is the opposition to current flow.