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Deloitte Interview Puzzles with Answers & Explanations

1. You have 3 boxes: Apples, Oranges, and Mixed. All are labeled incorrectly. How do you fix the labels by picking only one fruit?

Solution:
Pick from the Mixed box (which is wrong for sure).

  • If you pick an apple → that box is “Apples”
  • If you pick an orange → that box is “Oranges”

Then adjust remaining labels accordingly.

Concept: Logical deduction.


2. A man walks into a room with one matchstick and sees a lamp, a fireplace, and a candle. What does he light first?

Answer: The matchstick.
Explanation: He can’t light anything else before lighting the match.


3. Which weighs more: 1 kg of cotton or 1 kg of iron?

Answer: Both weigh the same.
Concept: Trick question.


4. A clock shows 3:15. What is the angle between the hour and minute hand?

Solution:
Minute hand = 90°
Hour hand at 3:15 = 3 × 30 + (15 × 0.5) = 97.5°
Difference = 7.5°


5. You have 9 identical balls, but one is heavier. Using a balancing scale, find the heavier one with minimum weighs.

Answer: 2 weighs.
Explanation:

  1. Divide into groups of 3 and weigh.
  2. Take heavier group, weigh 2 balls → heavier is found.

6. How can you measure exactly 4 liters using a 3-liter and 5-liter jug?

Steps:

  1. Fill 5L → pour into 3L (left 2L)
  2. Empty 3L → pour 2L into 3L
  3. Fill 5L again → pour until 3L is full (needs 1L)
    → 5L now has 4 liters.

7. A farmer has to cross a river with a fox, chicken, and corn. He can take one at a time. How?

Steps:

  1. Take chicken
  2. Return
  3. Take fox
  4. Bring chicken back
  5. Take corn
  6. Return
  7. Take chicken

8. If 5 machines make 5 products in 5 minutes, how long do 100 machines take to make 100 products?

Answer: 5 minutes.
Concept: 1 machine makes 1 product in 5 minutes.


9. What comes next? 2, 3, 5, 8, 12, 17, ?

Pattern: +1, +2, +3, +4, +5
Next = 17 + 6 = 23


10. You have two ropes that each burn in 60 minutes but burn unevenly. Measure 45 minutes.

Steps:

  1. Burn Rope A from both ends + Rope B from one end
    → Rope A burns in 30 mins
  2. After 30 mins, burn the other end of Rope B
    → Remaining burns in 15 mins
    Total = 45 minutes

11. Which is larger: 0.999… or 1?

Answer: They are equal.
Explanation: Infinite recurring decimals equal whole value.


12. You see a boat filled with people, but it’s not sinking. How?

Answer: They are married—“not single.”
Trick question.


13. You enter a room with 2 doors: Heaven and Hell. One guard always lies, one always tells truth. You can ask 1 question. What do you ask?

Ask: “Which door would the other guard say leads to Heaven?”
Explanation: Always choose opposite of the answer.


14. There are 8 coins. One is fake and lighter. Minimum weighs?

Answer: 2 weighs.
(Same logic as 9-ball puzzle.)


15. You have 100 doors initially closed. Every round you toggle doors (1st toggle all, 2nd toggle multiples of 2…). How many remain open?

Answer: 10 doors.
Explanation: Perfect squares remain open.


16. A car travels 60 km at 60 km/h. How fast must it go next 60 km to average 120 km/h total?

Answer: Impossible.
Explanation: First 60 km already took 1 hour. To average 120 km/h for 120 km, you need 1 hour total → you are out of time.


17. A man pushes his car to a hotel and loses money. Why?

Answer: He is playing Monopoly.


18. There are 3 switches outside a room with 3 bulbs inside. You can enter once. Identify which switch belongs to which bulb.

Steps:

  1. Turn switch 1 ON for 5 mins
  2. Turn switch 1 off, switch 2 ON
  3. Enter room
  • Warm bulb → switch 1
  • Lit bulb → switch 2
  • Off & cold → switch 3

19. How many times do the hands of a clock overlap in 12 hours?

Answer: 11 times
(They overlap a bit less than every 65 minutes.)


20. A boy has 7 red and 6 blue balls. Minimum picks to ensure 2 same color?

Answer: 3 picks (Pigeonhole principle)


21. If 12 cats catch 12 mice in 12 minutes, how many cats for 72 mice in 72 minutes?

Answer: 12 cats.
Explanation: 1 cat = 1 mouse in 12 min.


22. How many months have 28 days?

Answer: All 12 months.


23. A man is looking at a picture. “Brothers and sisters I have none, but the man’s father is my father’s son.” Who is in the picture?

Answer: His son.


24. You have 1 hourglass of 7 minutes and another of 11 minutes. Measure 15 minutes.

Steps:

  1. Start both
  2. When 7 ends, restart it (7 mins passed)
  3. When 11 ends, restart it (11 mins passed)
  4. When second 7 ends: 14 minutes
  5. 1 more minute remains in 11 → total = 15 minutes

25. You have 5 pirates dividing 100 coins. What does Pirate 1 propose?

Answer:
Pirate 1 gives 2 pirates 1 coin each to get majority vote.
Keeps 98 coins.


26. Fill in: 1, 4, 9, 16, 25, ?

Perfect squares → next is 36


27. A boy is 15 in 1990 and 10 in 1995. How?

Answer: Dates are BC (Before Christ).
Years count backward.


28. What starts with “T”, ends with “T”, and has T inside?

Answer: Teapot.


29. You cut a cake into 8 pieces using 3 cuts. How?

Explanation:

  1. First cut vertically
  2. Second cut horizontally
  3. Third cut horizontally through the center (layered)
    Gives 8 pieces.

30. A train takes 1 hour to travel from City A to B. Another takes 1 hour from B to A. Do they meet?

Answer: Yes, always.
Explanation: If they are on the same track & same time, they must cross paths.

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