i. In this case, the sample space is the set of all words of the length 3 written in the 2-letter alphabet {T,H}. This set contains= 8 words / elements {TTT, TTH, THT, THH, HTT, HTH, HHT, HHH}. ii. As it is formulated in the post, "Only the number of trials is of interest", the formal answer is "the space consists of one element, which is the number 3." // But I believe that the question is formulated incorrectly in this case.