Let
be the set of all positive integers that do not contain the digit
(base
). If
are arbitrary but distinct elements in
, prove that
%V0
Let $M$ be the set of all positive integers that do not contain the digit $9$ (base $10$). If $x_1, \ldots , x_n$ are arbitrary but distinct elements in $M$, prove that
$$\sum_{j=1}^n \frac{1}{x_j} < 80 .$$
Školjka