Question 21
Red and white tiles cover a square floor. The two floors below contain four and nine red tiles respectively. Each corner is always red, and every red tile is adjacent only to white tiles. If a floor has 25 red tiles, how many white tiles does it have?
Editorial task: derive the intended pattern answer, then test whether the written rules alone force it. Give a counterexample if they do not.
Original source options (retained):
(A) 25; (B) 39; (C) 45; (D) 56; (E) 72
Editorial format note: this essay examines the source wording and its assumptions. The original choices are retained for comparison.
Editorial task: derive the intended pattern answer, then test whether the written rules alone force it. Give a counterexample if they do not.
Original source options (retained):
(A) 25; (B) 39; (C) 45; (D) 56; (E) 72
Editorial format note: this essay examines the source wording and its assumptions. The original choices are retained for comparison.