Study guides › Level 9 · If–Then

Switches and lamps

Level 9 · for questions like “The lamp is on when switch A and switch B are both on. Otherwise it is off.”

💡 The idea

Each switch is on or off, so there are only a few cases. Try them all.

🪜 The steps

1. Write the rule.
2. Fill in what you know (switch A, the lamp).
3. Try switch B on, then off. Which matches the lamp?
4. If both match, you can’t tell.

⚠️ Watch out

• “A or B” includes both being on.
• “Exactly one” means one on and one off.

🎯 Try these

1. The lamp is on when A or B (or both) is on. If both are off, it is off. A is on and the lamp is on. What about B?

Answers: 1) Can’t tell

This guide is also in the 10LogicQ app: tap “📖 Study guide” after a puzzle.