CAT – questions and solution from progressions

Have given one interesting question from progressions. This question is from challenge quiz I. This is not that difficult, but as with all good questions, there is a formula-based method of solving this and there is a more straightforward intuitive way of solving them

Question 

Sum of first 12 terms of a GP is equal to the sum of the first 14 terms in the same GP. Sum of the first 17 terms is 92, what is the third term in the GP?

  1. 92
  2. -92
  3. 46
  4. 231
Correct Answer : 92. Correct Choice : (1)

Explanatory Answer
Sum of first 12 terms is equal to sum of first 14 terms.
Sum of first 14 terms = Sum of first 12 terms + 13th term + 14th term
=> 13th term + 14th term = 0

Let us assume 13th term = k, common ratio = r. 14th term will be kr.
k + kr = 0
k (1 + r) = 0
=> r = -1 as k cannot be zero

Common ratio = -1.
Now, if the first term of this GP is a, second term would be -a, third would be a and so on
The GP would be a, -a, a, -a, a, -a,…

Sum to even number of terms = 0
Sum to odd number of terms = a

Sum to 19 terms is 92 => a = 92
Third term = a = 92

————————————————————————-
2iim – CAT Classes, Correspondence material.

Related posts

  • CAT ProgressionsMay 31, 2013 CAT Progressions Question Second term of a GP is 1000 and the common ratio is   where n is a natural number. Pn is the product of n terms of this GP. P6 > P5 and P6 > P7, what is the sum of all […] Posted in Progressions
  • CAT – Trigonometry QuestionsAugust 6, 2013 CAT – Trigonometry Questions Question: 3sinx + 4cosx + r is always greater than or equal to 0. What is the smallest value ‘r’ can to take? A.  5 B.  -5 C.  4 D.  3 Correct Answer: […] Posted in Trigonometry
  • CAT Counting: Question with digitsMay 23, 2013 CAT Counting: Question with digits This is an interesting question from Counting. Simple framework, but one needs to be very careful with the enumeration. One can get wrong answers in a number of […] Posted in Combinatorics
  • CAT Online Coaching – Question from ProgressionsAugust 16, 2016 CAT Online Coaching – Question from Progressions Question Consider a set of numbers from 1 to 751. How many Arithmetic Progressions can be formed from this set of numbers such that the first term is 1 and the last term is 751 and the […] Posted in Progressions

Leave a Reply

Your email address will not be published. Required fields are marked *