The sample space of an experiment includes a set of different possibilities that can happen in the bounds of the experiment. A coin tossed once has two possibilities - heads or tails. When the coin is tossed five times, the sample space is 20: HHHHH, HHHHT, HHHTT, HHTTT, HTTTT, TTTTT, THHHH, TTHHH, TTTHH, TTTTH, THTHTH, HTHTHT, THHTT, THHHT, HTTTH, HTTHH, THHTT, etc.
