a. Show that in any set of n integers, there is a subset whose sum is divisible by n.

Question

b. Show that for any integer n, there is an integer whos digits (in decimal representation) consist of only 0 and 1.

I don't think the first can be proved. However, in a set of 2n-1 integers, it can be proved that there is a subset whose sum is divisible by n.

2. This makes no sense to me. Something is missing.