Analytical Puzzles
Hard
3 min
A code has four positions. The digits 1, 2, 3 and 4 are each used exactly once. Digit 1 is not first. Digit 4 is immediately before digit 2. Digit 3 is not last. What is the code?
Hint
Treat 4-2 as a block.
Answer
3-4-2-1.
Explanation
The block 4-2 can occupy positions 2-3 or 3-4. Since 1 cannot be first and 3 cannot be last, the valid arrangement is 3-4-2-1.
Step-by-Step Solution
4-2 must stay together.
3 cannot be position 4.
1 cannot be position 1.
Therefore 3-4-2-1 satisfies all constraints.
3 cannot be position 4.
1 cannot be position 1.
Therefore 3-4-2-1 satisfies all constraints.