Question 1
The number $2021=43\cdot47$ is composite. Prove that inserting any number of digits 8 between 20 and 21 gives another composite number. (4 points)
Neutral editorial illustration.
Practice scoring adds all whole-question scores (maximum 52). Official ITOT scoring adds only the three highest whole-question scores (maximum 30), after summing subparts within each question. The importer does not enforce best-three scoring. Duration: 300 minutes from historical organizer general rules, not an individually printed duration on this paper.
Neutral editorial illustration.
Practice scoring adds all whole-question scores (maximum 52). Official ITOT scoring adds only the three highest whole-question scores (maximum 30), after summing subparts within each question. The importer does not enforce best-three scoring. Duration: 300 minutes from historical organizer general rules, not an individually printed duration on this paper.