Crossing Bridge Interview Puzzle
Four people are on this side of the bridge. the bridge will be destroyed by a bomb in 17 minutes. everyone has to get across before that. Problem is that it’s dark and so you can’t cross the bridge without a flashlight, and they only have one flashlight. Plus the bridge is only big enough for two people to cross at once. The four people walk at different speeds: A fella is so fast it only takes him 1 minute to cross the bridge, B takes 2 minutes, C 5 minutes, the D it takes 10 minutes to cross the bridge. when two people cross the bridge together (sharing the flashlight),
they both walk at the slower person’s pace. can they all get across before the bridge blows up? Mentioning the speeds once again :
Person A: 1 minute
Person B: 2 minutes
Person C: 5 minutes
Person D:10 minutes
Of course its possible, otherwise it wouldn’t be a very interesting question. The only trick is in realizing that you want to get the two slowest people across together, because otherwise you are wasting too much time. Then once you get them across, how do you not make one of them walk back with the flashlight. Well, you just have one of the fast people already there waiting to sprint the flashlight back across.1. A & B cross. total time: 2 minutes.
C ,D |==========================| A,B(flash light)
2. B comes back. total time: 4 minutes.
C,D,B(FL)|==========================| A
3. C & D cross. total time: 14 minutes.
B |==========================| A,C,D(FL)
4. A comes back. total time: 15 minutes.
B,A(FL)|==========================| C ,D
5. A & B cross. total time: 17 minutes.
|========= =============| A,B,C,D
DONE
Your Answer
More puzzles to try-
Number of people in the bus puzzle
An empty bus pulls up to a stop and 10 people get on, 8 took ticket and rest 2 shown ...Read More »The Monkey and the Coconut
Ten people land on a deserted island. There they find lots of coconuts and a monkey. During their first day ...Read More »What made her suspicious of that man?
A girl was sitting in her hotel room when she heard a knock on the door. She opened the door ...Read More »Never Falls
Iron roof, glass walls, burns and burns never falls!!!Read More »Killer’s Suspense
The richest man in the city Mr Rechard is kidnapped. James Bond is appointed to the case. At the crime ...Read More »What happened to the remaining $1?
Three guests check into a hotel room. The clerk says the bill is $30, so each guest pays $10. Later ...Read More »A lot of people don’t like me puzzle
I am something, a lot of people don’t like me, including you. But I’m called upon anytime one is injured. ...Read More »Make two words riddle
Add an English word to the following set of words in such a way that the first word is completed ...Read More »The Chicken and Leg Problem
A chicken farmer also has some cows for a total of 30 animals, and the animals have 74 legs in ...Read More »Coffee, milk, chocolate, mozzarella and jam for breakfast riddle
It’s 7 o’clock in the morning, you are still sleeping in bed and you hear your friends knocking at the ...Read More »NDA Exam 2013 – Find the missing Number?
Which number replaces the question mark?Read More »Which coat would go on the second?
Mr. Hero Honda decided to give his bike 3 coats of paint. Which coat would go on the second?Read More »How to Cross River
2 ladies and 2 girls need to cross a river in a boat big enough for 1 LADY or 2 ...Read More »Coin Head and Tail
I have two coins. * One of the coins is a faulty coin having a tail on both sides of ...Read More »Can you name it ?
There is a five letter word which has 3 consonants(all are same) and 2 different vowels. Also something wrong associated ...Read More »Red and Blue Marbles
You have two jars, 50 red marbles and 50 blue marbles. You need to place all the marbles into the ...Read More »In a fair
As I was going to the fair, I saw a man with golden hair. He had 3 sons each with ...Read More »Count The Blocks
Can you count the number of blocks in the picture below?Read More »Baseball Game
Alex wants to go home but can’t, because the man in the mask is waiting for him. What is going ...Read More »i am beautiful
I am pretty beautiful, fluttering in the pale-blue sky. Delicate, fragile on the wing, indeed I am a pretty thing. ...Read More »