Let S be the set of all real numbers of the form
(a_1)/(3) + (a_2)/(3^2) + (a_3)/(3^3) + ...
where (a_i) is equal to either 0 or 1 or 2 for each i.
(a) Is the number 1/4 in the set S?
(b) Is the number 1/7 in the set S?
+837 
