Interview Question: The Heaviest Ball
You have eight balls all of the same size, 7 of them weigh the same, and one of them weighs slightly more.
How can you find the ball that is heavier by using a balance and only two weighings?
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
- Take 6 of the 8 balls and put 3 on each side of the scale. If the heavy ball isn’t in the group of 6, you know it’s one of the remaining 2 and so you put those two in the scale and determine which one.
- If the heavy ball is in the 6, you have narrowed it down to 3. Of those 3, pick any 2 and put them on the scale. If the heavy ball is in that group of 2, you know which one it is. If both balls are of equal weight, then the heavy ball is the one you sat to the side.
Note: For this problem solving job interview question, there is an actual logical 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 (e.g., Microsoft, Google, Goldman Sachs)
- 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?