Problem 12 · Symmetry · 4 points
Made by AI and not reviewed by a real person.
Lulu hangs 7 lanterns in a row. Each is lit or dark, the lit-and-dark order is the same from either end, and exactly 3 lanterns are lit. Counting from the left, which lantern must be lit?
- 4th
- 1st
- 5th
- 2nd
- 3rd
Show a hint
- Match lanterns at opposite ends.
- What is different about the middle lantern?
Show the answer and solution
Answer: A — 4th
The lanterns on either side of the middle match in pairs. So two of the lit lanterns make a pair, and the third must be the middle, 4th lantern. The 1st lantern might be lit, but it need not be: the lit pair could be the 2nd and 6th lanterns instead.