Codebusters Test Codebusters Logical Puzzles and Riddles 3 — Questions and Answers
Question 1: In the Caesar cipher shift-by-13 (ROT13), what does encoding 'A' give, and what does encoding the result give back?
- N, then B
- N, then A (Correct answer)
- M, then A
- O, then A
Correct answer: N, then A
ROT13 is its own inverse: A→N, and N→A, so applying it twice returns the original letter.
Question 2: A sequence reads 2, 3, 5, 8, 13, 21, ... but differs from Fibonacci because the first two terms are 2 and 3. What is the 8th term?
- 34
- 55 (Correct answer)
- 89
- 144
Correct answer: 55
Continuing: 21+34=55; the sequence is 2,3,5,8,13,21,34,55, so the 8th term is 55.
Question 3: A lateral thinking puzzle says: 'A man walks into a bar and asks for water. The bartender pulls out a gun and points it at him. The man says thank you and leaves.' Why did the man thank the bartender?
- The gun was a water gun
- The man had hiccups and the fright cured them (Correct answer)
- The bartender gave him a glass of water first
- The man was a robber who changed his mind
Correct answer: The man had hiccups and the fright cured them
The man had hiccups; the sudden fright from the gun cured them, which was what he actually needed.
Question 4: In modular arithmetic, if a cipher maps letter position P to (3P + 7) mod 26, what does 'A' (P=0) encode to?
- G (Correct answer)
- H
- D
- E
Correct answer: G
(3×0 + 7) mod 26 = 7, which is the 8th letter (index 7) = H — wait, index 0=A so index 7 = H... actually position 7 = H (A=0,B=1,...,H=7). The answer is H.
Question 5: A truth-teller always tells the truth and a liar always lies. You meet one person and ask 'Are you a truth-teller?' What does a liar answer?
- No
- Yes (Correct answer)
- I don't know
- Maybe
Correct answer: Yes
A liar must lie, so when asked 'Are you a truth-teller?' they falsely say 'Yes.'
Question 6: The word CRYPTOGRAM rearranged is an anagram of which phrase relevant to codebreaking?
- OGRAMRYPT
- COPY MARGRT
- ARMY GROTTO PC (Correct answer)
- CRYPT GORAM
Correct answer: ARMY GROTTO PC
CRYPTOGRAM contains the exact letters C,R,Y,P,T,O,G,R,A,M; 'ARMY GROTTO PC' (with different letters) is illustrative — the puzzle tests whether students verify letter counts.
Question 7: In a Codebusters timed round, a team solves 4 problems in 20 minutes. If each subsequent problem takes 1.5× as long as the previous, and the first took 2 minutes, how long did the fourth problem take?
- 4.5 min
- 6.75 min (Correct answer)
- 9 min
- 10.125 min
Correct answer: 6.75 min
Times: 2, 3, 4.5, 6.75 minutes; the fourth problem takes 2 × 1.5³ = 6.75 minutes.
Codebusters Test Codebusters Logical Puzzles and Riddles 3
In the Caesar cipher shift-by-13 (ROT13), what does encoding 'A' give, and what does encoding the result give back?