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Citi Quantitative Analyst Interview Question (student candidate)

"You have 99 distinct numbers from 1-100, how would you find which number is missing?"
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Answers & Comments

0
of 2
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Depends on whether the numbers are sorted or not.
- Interview Candidate on Oct 28, 2010 Flag Response
0
of 1
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I would average them out and multiply their difference from 50.5 by 100 to find the missing number
- honeyoak on Feb 19, 2011 Flag Response
2
of 2
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I would calculate total and substract it from total of full list.

Example:
Calculate total for original list 1,2,3,4,..100 = 5050
Let's assume the missing mnumber is 20
Calculate total of given list = 5030
The missing number is 5050 - 5030 = 20
- kebzor on May 1, 2011 Flag Response
0
of 0
votes
kebzor is correct. same principle applies to any list of consecutive n integers (starting from 1). e.g. if list is 1-10, then sum is 55 so the missing number x = 55 - (sum of given nine numbers). side question: what if you are missing two numbers from 1-10; what can you say?
- anon on May 16, 2013 Flag Response
0
of 0
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in fact, as long as the list is of finitely many consecutive distinct integers, the above method works. using factorization, there is also a unique solution to solving for two missing numbers. i don't know of an elegant solution for k missing numbers in general.
- anon on May 16, 2013 Flag Response

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