HKIMO 2020 Grade 5 National Final (Heat) Set 01 Question 25

Numbers are drawn from the 80 integers 20 through 99. At least how many must be drawn to guarantee two numbers whose sum is 85?

Source glossary (English–Vietnamese): Integer: số nguyên; At least: ít nhất; Random: ngẫu nhiên; Ensure: chắc chắn; Sum: tổng.