perplexus.info :: Logic : Five People on Two Bridges

Five People on Two Bridges (Posted on 2005-06-25)

In the puzzle Four people on a Bridge we met four people who needed to cross a bridge at night. In this puzzle, there are five people who must cross two sequential bridges at night. As in the original puzzle, there are some hindrances:

The bridges can only support two people crossing at a time.

Each person has a different speed in which they can cross: 10 minutes, 7 minutes, 5 minutes, 2 minutes, and 1 minute.

They have only two flashlights to share among them.

What is the shortest amount of time it will take for all five people to cross both bridges?

See The Solution Submitted by Erik O.

Rating: 3.8000 (5 votes)

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Puzzle Solution

Comment 41 of 41 |

The shortest amount of time it will take for all five people to cross both bridges is 27 minutes.

Let us label the 5 persons respectively as:

A (10 miutes), B (7 minutes), C (5 minutes), D (2 minutes), and E (1 minute).

Then, the procedure is furnished hereunder as follows:

(i) D and E cross the first bridge : T(0) to T(2)

(ii) A and B cross the first bridge: T(2) to T(12)

(iii) D and E cross the 2nd bridge: T(2) to T(4)

(iv) E returns to the middle: T(4) to T(5)

(v) A and B cross the 2nd bridge: T(12) to T(22)

(vi) E returns to the starting point: T(12) to T(13)

(vii) C and E cross the 1st bridge: T(13) to T(18)

(viii) C and E cross the 2nd bridge: T(22) to T(27)

Posted by K Sengupta on 2022-07-19 23:59:25

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