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UPSC 2009: While adding the first few continuous natural numbers, a candidate missed one of the numbers and wrote the answer as 177. What was the number missed?
(a)11
(b)12
(c)13
(d)14
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Not attemptedCorrect Answer: (c) 13
Sum of the first n natural numbers is Sₙ = n(n+1)/2. We need Sₙ − m = 177, where m is the missed number. Trying n = 19 gives S₁₉ = 190, so m = 190 − 177 = 13, which matches option (c). ([selfstudyhistory.com](https://selfstudyhistory.com/2015/04/12/prelims-ias-general-studies-solved-paper-with-explanations-2009-part-2/?utm_source=openai))
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Frequently Asked Questions
What is the correct answer to this UPSC 2009 Science & Technology question?▼
The correct answer is option (c): 13. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Quantitative Aptitude question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2009, GS Paper 1, as Question 100. It falls under Science & Technology > Quantitative Aptitude.
What is the difficulty level of this UPSC question?▼
This question is rated "easy". It tests basic recall and most well-prepared aspirants should answer it correctly.
How many UPSC Prelims questions have been asked from Quantitative Aptitude?▼
UPSC has asked 178 questions from Quantitative Aptitude (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.