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Introduction
Puzzles are good exercise for the brain. They help in enhancing the cognitive abilities of the brain helping with Problem Solving and related skills. There are numerous types of puzzles; each one having a logic inherent to itself which helps in cracking it. A good puzzle well is actually like a good mystery that we may have read about or watched on TV. It has the finest of hints which help in reaching its solution.
The following article discusses one such puzzle so let's get right to it.
Puzzle Description
The puzzle is as follows:
Albert and Bernard just become friends with Cheryl, and they want to know when her birthday is. Cheryl gives them a list of 10 possible dates:
May 15, May 16, May 19
June 17, June 18
July 14, July 16
August 14, August 15, August 17
Cheryl then tells Albert and Bernard separately the month and the day of her birthday respectively.
Albert: I don't know when Cheryl's birthday is, but I know that Bernard doesn't know too.
Bernard: At first I don't know when Cheryl's birthday is, but I know now.
Albert: Then I also know when Cheryl's birthday is.
Cheryl gives Bernard and Albert a list of 10 possible dates for her birthday.
May
15
16
19
June
17
18
July
14
16
August
14
15
17
Our approach in this solution is to eliminate the impossible dates based on the conversation between Bernard and Albert.
Albert:I don’t know when Cheryl’s birthday is, but I know that Bernard doesn’t know too.
Albert knows the month correctly, and Bernard knows the day. Bernard would have correctly known Cheryl’s birthday if the date was 18 or 19, as these dates occur only once. The fact that Albert knows that Bernard doesn’t know the birthday proves that the birthday is either in July or in August.
The remaining options are:
July
14
16
August
14
15
17
Bernard: At first I didn’t know when Cheryl’s birthday is, but I know now.
After eliminating the choices, Bernard knows the birthday correctly. This is possible only if the day is either 15, 16, or 17, as these occur only once in the remaining options. If it would’ve been 14, Bernard could not guess the birthday correctly as it appears twice.
After eliminating the choices:
July
16
August
15
17
Now, finally, Albert says:
Albert: Then I also know when Cheryl’s birthday is.
Looking at the remaining options, we can see that we have only August and July left, with August having two possible dates and July having only one possible date.
Albert said that he now knows when the birthday is. It is possible only if the month is July as August has two possible options.
Therefore, the answer to this puzzle is July 16.
Answer: July 16
Frequently Asked Questions
What are some of the tips for solving puzzles during an interview?
Always ask for clarifications if you feel that you do not understand the puzzle entirely. Getting the right answer is not as important as your approach. Always explain your approach while answering.
Why are puzzles asked in interviews?
To check the analytical and problem-solving skills of the candidate.
Should we always reach the correct answer to the puzzle during the interview?
You should focus on your approach and your ability to convey it to the interviewer. Sometimes, you may not be able to reach the correct answer, but if your approach is right, it does not matter much.
Conclusion
This blog talked about a very interesting puzzle called Cheryl’s birthday puzzle. We looked at its solution extensively. This is just one of the numerous puzzles that can be asked in your interviews. You can solve any puzzle asked in your interview if you keep practicing these types of puzzles.
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