Let the families f1,  f2, , f10  have 3, 4, 3, 2, 5, 4, 3, 6, 4, 5 members, respectively Let us select a family and note down the number of members in the family denoting
X Clearly, X is a random variable defined as below :
X(f1) = 3, X(f2) = 4, X(f3) = 3, X(f4) = 2, X(f5) = 5,
X(f6) = 4, X(f7) = 3, X(f8) = 6, X(f9) = 4, X(f10) = 5
Thus, X can take any value 2,3,4,5 or 6 depending upon which family is selected