Interview Question: The Bridge Crossing
There are 4 friends (Jay Leno, David Letterman, Jon Stewart and Stephen Colbert). They must cross a narrow unstable bridge at night. You must use a flashlight to cross the bridge and they only have 1 flashlight. No more than 2 people can cross at any time and the faster one can not carry the slower one. Leno can cross in 1 minute, Letterman in 2 minutes, Jon Stewart in 5 minutes, and Stephen Colbert in 10 minutes. They only have 17 minutes for all of them to cross the bridge. How should they do it?
Strategy and Approach to Answering a Problem Solving Interview Question
If you get asked a problem solving question in an interview, remember that they are NOT looking for the RIGHT answer. They are evaluating the approach you use to think out and solve the problem. A strong candidate demonstrates the following:
- Evaluates and understand the scope of the problem
- Communicates assumptions
- Demonstrates quantitative analytical skills
- Answers the question that has been asked. You’d be surprised how many candidates get lost in the analysis and solve for a different question than what was asked.
How to Answer this Problem Solving Interview Question
In evaluation, we have the time it takes for each to walk across and we have the time limit. Thinking out loud, we can see that we can’t send them over individually, and we can’t group the faster guys with the slower guys because there’s not enough time. We need to group the two slowest guys together, but we can’t send them over first because we will run out of time.
The solution is:
- Send Leno and Letterman over the bridge together (2 minutes)
- Have Leno come back with the flashlight (2+1 = 3 minutes)
- Send the two slowest guys across the bridge (3+10=13 minutes)
- Have Letterman come back with the flashlight (13+2= 15 minutes)
- Finally send Leno and Letterman to cross together again (15+2 = 17 minutes)
Note: For this problem solving job interview question, there is an actual mathematical answer, however the interviewer will want to evaluate your thinking process. In answering the interview question, the lead up to your answer will be just as important as the actual answer itself.
For more problem solving, brain teasers, riddles, puzzles, logic job interview questions, please check our out Problem Solving Interview Section.
List of Problem Solving Interview Questions used by top Firms, such as Microsoft, Google, IBM, etc.
- 100 Prisoners and a Light Bulb Interview Question
- 5 Pirates and 100 Gold Coins Interview Question
- Birthday Problem Interview Question
- Bridge Crossing Interview Question
- Burning Rope Interview Question
- Card Game Interview Question
- Crossing the River Interview Question
- Dog Show Interview Question
- Equal Halves of Rectangular Birthday Cake Interview Question
- Estimate the market demand in gallons for skim milk consumed in the U.S. in a given year.
- How many golf balls can you fit in a school bus?
- How many street lamps are there in Manhattan?
- How many times a day does a clock’s hands overlap?
- How Many Zeros in 100 Factorial (100!)?
- How much would you charge to wash all the windows in New York City?
- In a country, in which every family wants a boy
- Rising Tide Interview Question
- The Fermi Problem – How many Piano Tuners are there in Chicago?
- The Heaviest Ball Interview Question
- The Monty Hall Interview Question
- The Race Interview Question
- Tiger and Sheep Interview Question
- Why are manhole covers round?