Let
be distinct positive integers and let
be a set of
positive integers not containing
A grasshopper is to jump along the real axis, starting at the point
and making
jumps to the right with lengths
in some order. Prove that the order can be chosen in such a way that the grasshopper never lands on any point in
Proposed by Dmitry Khramtsov, Russia
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Let $a_1, a_2, \ldots , a_n$ be distinct positive integers and let $M$ be a set of $n - 1$ positive integers not containing $s = a_1 + a_2 + \ldots + a_n.$ A grasshopper is to jump along the real axis, starting at the point $0$ and making $n$ jumps to the right with lengths $a_1, a_2, \ldots , a_n$ in some order. Prove that the order can be chosen in such a way that the grasshopper never lands on any point in $M.$
Proposed by Dmitry Khramtsov, Russia