Track / Stage 4 / 179 of 340 #439 of 1964

Problem 439

AMC 12 late, AIME early

Number theory Difficulty 4.8 Find the answer

Given $\varnothing \varsubsetneqq M \subseteq \mathbf{N}$ , and if $x \in M$ , then $6-x \in M$ , then the set $M$ can contain at most
$\qquad$ elements

Your answer

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Official solution

(3) 7

Source: NuminaMath-1.5, licensed Apache-2.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.