CAT Quantitative Aptitude Questions | CAT Number Theory - Sum of first N natural numbers

CAT Questions | Number Theory | Sum of first N numbers

The question is about Sum of first N natural numbers. Application of sum of first N numbers. We need to do trial and error to arrive at the answer. Dealing with digits and base system of a number is a vital component in CAT Number Theory. A range of CAT questions can be asked based on this simple concept in the CAT Exam.

Question 2: A page is torn from a novel. The sum of the remaining page numbers is 10000. What are the two page-numbers on the torn page of this novel?

  1. 77 and 78
  2. 33 and 34
  3. 8 and 9
  4. None of these

Best CAT Online Coaching
Try upto 40 hours for free
Learn from the best!


2IIM : Best Online CAT Coaching.


Best CAT Coaching in Chennai


CAT Coaching in Chennai - CAT 2021
Online Batches Available Now!


Explanatory Answer

Method of solving this CAT Question from Number Theory - Digits: Number Theory questions make us go from rigour to trial-and-error alternately. This is one such question.

\\frac{n(n+1)}{2}\\) should be nearby 10,000, so n (n + 1) is somewhere near 20,000.
So n should be around √(20000) about 141.
Try 142
\\frac{142 * 143}{2}\\) = 10153
\\frac{141 * 142}{2}\\) = 10011
So, the missing pages are either 76 and 77 or 5 and 6.

The question is "What are the two page-numbers on the torn page of this novel?"

Hence the answer is "None of these"

Choice D is the correct answer.

 


CAT Online Coaching | CAT Number Systems questions Videos On YouTube


Other useful sources for Number System Questions | Number Theory HCF and LCM Sample Questions


CAT Questions | CAT Quantitative Aptitude

CAT Questions | CAT DILR

CAT Questions | Verbal Ability for CAT


Where is 2IIM located?

2IIM Online CAT Coaching
A Fermat Education Initiative,
58/16, Indira Gandhi Street,
Kaveri Rangan Nagar, Saligramam, Chennai 600 093

How to reach 2IIM?

Phone: (91) 44 4505 8484
Mobile: (91) 99626 48484
WhatsApp: WhatsApp Now
Email: prep@2iim.com