The torch has a remaining battery life of only 30 seconds. When Assume that a solution minimizes the total number of crossings. The time taken for each member is as shown:Logic puzzles require you to think. Also, it is impossible for them to cross together last, since this implies that one of them must have crossed previously, otherwise there would be three persons total on the start side.
It takes 30 minutes to cross the bridge (walk or run) - For the purpose of the riddle.
An interesting puzzle where 4 people must cross a bridge in 17 minutes. So, since there are only three choices for the pair-crossings and C and D cannot cross first or last, they must cross together on the second, or middle, pair-crossing. This gives us, B+A+D+B+B = 2+1+8+2+2 = 15. Remember our assumption at the beginning states that we should minimize crossings and so we have five crossings - 3 pair-crossings and 2 single crossings. A and B are now on the start side and must cross for the last pair-crossing. This gives a total of five crossings - three pair crossings and two solo-crossings. intertwingly.net: Sam Ruby: Bridge Crossing Puzzle (2006 March 3) (includes a comment by me) 'Four men want to cross a bridge.
In this version of the puzzle, A, B, C and D take 5, 10, 20, and 25 minutes, respectively, to cross, and the time limit is 60 minutes. The only light available was a lamp which could only burn for 30 minutes. The guards take the break at the same time. (Here we use A because we know that using A to cross both C and D separately is the most efficient.) Different members take different amount of time to cross and the time they take must be at the pace of the slower one. the question can be generalized for N people with varying individual time taken to cross the bridge. C takes 5 minutes to cross the bridge. The only light available was a lamp which could only burn for 30 minutes. How would you get across the bridge?
Hence, they will cross separately.
D takes 8 minutes to cross the bridge. It is one of the category of river crossing puzzles, where a number of objects must move across a river, with some constraints. They want to cross the bridge. When two people cross the bridge together, they must move at the slower person's pace. Putting all this together, A and B must cross first, since we know C and D cannot and we are minimizing crossings.
It is a dark night and there is a family of 5 that needs to cross a bridge suspended over a deep valley. Then we choose to send the fastest back, which is B. Without a torch, they cannot proceed. Several variations exist, with cosmetic variations such as differently named people, or variation in the crossing times or time limit.The puzzle is known to have appeared as early as 1981, in the book In the case where there are an arbitrary number of people with arbitrary crossing times, and the capacity of the bridge remains equal to two people, the problem has been completely analyzed by Martin Erwig from Oregon State University has used a variation of the problem to argue for the usability of the Haskell programming language over Prolog for solving The puzzle is also mentioned in Daniel Dennett's book Basically, the two fastest people cross together on the 1st and 5th trips, the two slowest people cross together on the 3rd trip, and EITHER of the fastest people returns on the 2nd trip, and the other fastest person returns on the 4th trip.
A maximum of only two persons can cross at one time, and they must have the lamp with them. This strategy makes A the torch bearer, shuttling each person across the bridge:This strategy does not permit a crossing in 15 minutes.
The bridge and torch problem (also known as The Midnight Train and Dangerous crossing ) is a logic puzzle that deals with four people, a bridge and a torch. John and his family members want to cross to the other side of the bridge at night. Thus the minimum time for four people is given by the following mathematical equations: Logical puzzles, Hard puzzles, ... One can cross the bridge in 1 minute, another in 2 minutes, ... Abhishek on September 30, 2015 at 6:22 pm said: 17 is the right answer :-First 1 and 2 will go – 2 minute. Each person walks at … But then C or D must cross back to bring the torch to the other side, and so whoever solo-crossed must cross again. The torch needs to be returned to the remaining persons. They have only one lamp which lasts for only 30 minutes. The bridge is of a width such that a maximum of 2 people may cross at a time. Five persons are standing on one side of a bridge. Puzzle: There are 4 persons (A, B, C and D) who want to cross a bridge in night. Up to two members can cross each time. Bridge Crossing 2, Math Puzzles. A takes 1 minute to cross the bridge.
Also, assume we always choose the fastest for the solo-cross. They have one torch and, because it's night, the torch has to be used when crossing the bridge. First, we show that if the two slowest persons (C and D) cross separately, they accumulate a total crossing time of 15. Four people come to a river in the night. There is a bridge. This question was however popularized after its appearance in the book "How Would You Move Mount Fuji?" The question is, can they all get across the bridge if the torch lasts only 15 minutes?An obvious first idea is that the cost of returning the torch to the people waiting to cross is an unavoidable expense which should be minimized. The guards take 1, 15 minute break every day (only once!). B takes 2 minutes to cross the bridge. Bridge Crossing Thanks Ranish. You will have to be logical in your reasoning.The brother helps well in bringing the lamp to and fro with his speed. A popular math based puzzle game that requires logic to solve.It is a dark night and there is a family of 5 that needs to cross a bridge suspended over a deep valley. They all take different times to cross the bridge, 1, 2, 5, & 10 minutes and must cross in pairs with a torch. Assume that C and D cross first. Crossing the Bridge puzzle asked in job interview.
Then, A must cross next, since we assume we should choose the fastest to make the solo-cross. Up to two members can cross each time. Two guards stand to guard the bridge, one at each end to stop anyone from crossing at any side.