-- If the four light bulbs are in series, then the total resistance becomes four times as much as it was with a single bulb, because now, the current has to push through one light bulb four times.
-- If the four light bulbs are in parallel, then the total resistance becomes 1/4 as much as it was with a single bulb, because now, the current can split up into four equal streams, and each stream only has to push through a single light bulb.
