The sample space for the given experiment contains all the possible outcomes, namely the distinct letters making up the word mathematics.
Ω={m,a,t,h,e,i,c,s}

Sample space is all possible outcomes
It is a set of all possible outcomes of an experiment. It is denoted by S.
S=[m,a,t,h,e,m,a,t,i,c,s] so here you have 11 letters.