1. You have a 3-gallon jug and a 5-gallon jug, and your goal is to measure out exactly 4 gallons of water. How do you do it?
2. You are given a set of scales and 12 identical-looking balls. One of the balls is slightly heavier than the others. How can you find the heavier ball using the scales only three times?
3. You have a 9x9 Sudoku grid. Each row, column, and subgrid must contain the numbers 1 through 9 without repetition. How do you solve the Sudoku puzzle?
4. You have eight balls, and one is slightly heavier than the others. You also have a balance scale. What is the minimum number of weighings needed to find the heavier ball?
5. You are in a room with three light switches, each controlling a different light bulb in the next room. How can you determine which switch corresponds to which bulb, if you are only allowed to enter the next room once?
6. You have a rope that takes exactly one hour to burn from end to end. The rope does not burn at a consistent rate. How can you use the rope to measure exactly 45 minutes?
7. You have 12 marbles that appear identical, but one is slightly heavier than the others. How can you find the heavier marble using a balance scale in only three weighings?
8. You have a 5-liter jug and a 3-liter jug, and your goal is to measure out exactly 4 liters of water. How do you do it?
9. You have a 7-minute hourglass and an 11-minute hourglass. How can you measure exactly 15 minutes?
10. You have a 4x4 grid with some cells filled with numbers from 1 to 4. Each row and each column must contain each number exactly once. How do you complete the grid?