Explanation:
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First you must know that a tossed coin can only produce a head (H) and a tail (T).
Sample space S1 = {H T}
When two coins are tossed, the possible outcomes are gotten by mapping another {H, T} to the previous sample space to have;
S2 = {HH, HT, TH, TT}
For three coin, the possible outcomes are gotten by mapping {H, T} to the previous sample space {HH, HT, TH, TT}to get S3
S3 = S1 × S2
S3 = {HHH, HHT HTH, HTT, THH, THT, TTH, TTT}
Hence the sample space of the experiment of tossing 3 coins is {HHH, HHT HTH, HTT, THH, THT, TTH, TTT}
n(S3) = 8
b) From the sample space, you can see that the event having the first toss as a tail are E = {THH, THT, TTH, TTT}
n(E) = 4