The Bridge and Torch Puzzle is one of the most famous logic riddles. It combines strategy, timing, and optimization. Four people must cross a dangerous bridge at night, but the constraints make the problem tricky. At first glance, it seems like guesswork, but with the right strategy, all four can cross safely within a limited time.

This puzzle is popular in interviews, brain teasers, and logic competitions, as it tests planning, sequential thinking, and teamwork.

Bridge and Torch Puzzle Setup and Rules

Here’s how the puzzle works:

• Four people need to cross a bridge at night.
• Only two people can cross at a time.
• There is one torch, and the bridge is too dangerous to cross without it.
• The torch must always be carried, and it cannot be thrown across.

Individual Crossing Times:

• Person A: 1 minute
• Person B: 2 minutes
• Person C: 5 minutes
• Person D: 10 minutes

Movement Rule:
When two people cross together, they must go at the slower person’s pace.

Objective:
All four must cross the bridge within 17 minutes or less.

How to Solve the Bridge and Torch Puzzle?

The key to solving this puzzle is optimizing the crossings, especially minimizing the number of trips for the slowest individuals. The solution uses the fastest people to shuttle the torch back and forth efficiently.

Step 1: First Crossing (A and B)

• Who crosses: Person A (1 min) and Person B (2 min)
• Time taken: 2 minutes (Person B’s speed)
• Status: Person A and B are across; Person C and D are on the starting side
• Time elapsed: 2 minutes

Step 2: Return Trip (A returns with the torch)

• Who returns: Person A (1 min)
• Time taken: 1 minute
• Status: Person A is back on the starting side; Person B waits across
• Time elapsed: 3 minutes

Step 3: Second Crossing (C and D)

• Who crosses: Person C (5 min) and Person D (10 min)
• Time taken: 10 minutes (Person D’s speed)
• Status: Person C and D are across; Person A and B on starting side
• Time elapsed: 13 minutes

Step 4: Return Trip (B returns with the torch)

• Who returns: Person B (2 min)
• Time taken: 2 minutes
• Status: Person B is back on starting side; Person C and D wait across
• Time elapsed: 15 minutes

Step 5: Final Crossing (A and B)

• Who crosses: Person A (1 min) and Person B (2 min)
• Time taken: 2 minutes (Person B’s speed)
• Status: All four, A, B, C, D, have crossed the bridge
• Time elapsed: 17 minutes

Visual Summary:

Trip Number	Who Crosses	Time Taken	Status After Trip
1	A & B	2 min	A & B across, C & D start side
2	A returns	1 min	A back, B across, C & D start side
3	C & D	10 min	C & D across, A & B start side
4	B returns	2 min	B back, A & B start side, C & D across
5	A & B	2 min	All across

Key Strategy Points

• The slowest members (C and D) cross the bridge only once.
• The fastest member (A) makes multiple trips to minimize overall time.
• The puzzle is solved in exactly 17 minutes, achieving the goal.

Final Answer: Efficient Bridge Crossing Strategy

By following the A & B first, A returns, C & D cross, B returns, A & B final sequence:

• All four people cross safely.
• Total time = 17 minutes.

This puzzle highlights the importance of sequencing, optimization, and logical reasoning — skills useful in problem-solving, programming, and real-life planning.

Why the Bridge and Torch Puzzle is Popular?

This puzzle is a classic because it illustrates optimal strategy and teamwork. It is widely used in:

• Job interviews for top companies
• Math and logic competitions
• Puzzle books and online brain teasers

It demonstrates how careful planning can overcome time constraints and risky situations.

Similar Logic Puzzles with Answers

1. River Crossing Puzzle – Farmer, Goat, Wolf, Cabbage

Setup: A farmer must transport a goat, wolf, and cabbage without anything getting eaten.
Answer: The sequence Goat → Wolf → Cabbage → Goat ensures safe crossing.

2. 100 Prisoners Hat Puzzle – Parity Logic

Setup: 100 prisoners must guess their hat color.
Answer: Using parity, 99 prisoners always survive, sometimes all 100.

3. Monty Hall Problem – Probability Optimization

Setup: Pick one of three doors; one hides a car.
Answer: Switching increases winning probability from 1/3 to 2/3.

4. Blue Eyes Puzzle – Logical Deduction

Setup: Islanders discover their eye color based on others’ actions.
Answer: All with blue eyes leave on the nth night, deducing their color.