💼 Job interview logic puzzles with full solutions

1. Three boxes are labeled "Apples," "Oranges" and "Mixed." Every label is wrong. You may take out one fruit from one box without looking inside. How do you fix all the labels?

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2. You have two ropes. Each burns for exactly one hour, but unevenly - half of a rope might burn in 5 minutes and the rest in 55. How do you measure exactly 45 minutes?

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3. You have 8 balls that look the same. One is slightly heavier. Using a balance scale only twice, how do you find the heavy ball?

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4. Three switches outside a closed room control three light bulbs inside. You can flip the switches as much as you like, but you can enter the room only once. How do you tell which switch controls which bulb?

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5. 100 doors in a hallway are closed. Person 1 opens every door. Person 2 toggles every 2nd door, person 3 every 3rd door, and so on up to person 100. How many doors are open at the end?

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6. You have a 3-gallon jug, a 5-gallon jug and unlimited water. How do you measure exactly 4 gallons?

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7. Four people must cross a bridge at night with one flashlight. At most two can cross at once, and anyone crossing needs the flashlight. They take 1, 2, 5 and 10 minutes, and a pair moves at the slower person's speed. What is the shortest total time?

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8. You have 25 horses and a track that fits 5 at a time. There is no stopwatch - you only see the finishing order. What is the fewest races needed to find the 3 fastest horses?

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9. You have two identical eggs and a 100-story building. What is the fewest drops that guarantees you find the highest floor an egg can survive, even in the worst case?

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10. How many times a day do the hour and minute hands of a clock overlap?

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11. What is the angle between the hour and minute hands at 3:15?

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12. In a dark room, a drawer holds 10 black socks and 10 white socks. How many socks must you take out to be sure you have a matching pair?

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13. You have a coin that may be biased, and you don't know which way. How can you use it to make a perfectly fair 50-50 choice?

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14. Why are manhole covers round?

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15. How many zeros are at the end of 100! (100 factorial)?

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16. Two trains are 100 miles apart and head toward each other at 50 mph each. A fly starts at one train and zips back and forth between them at 75 mph until they meet. How far does the fly travel?

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