How many terms of G.P. 3, 32, 33, &helli | Class 11 Mathematics Chapter Sequence and Series, Sequence and Series NCERT Solutions

Welcome to the NCERT Solutions for Class 11 Mathematics - Chapter Sequence and Series. This page offers a step-by-step solution to the specific question from Exercise 3, Question 13: . With detailed answers and explanations for each chapter, students can strengthen their understanding and prepare confidently for exams. Ideal for CBSE and other board students, this resource will simplify your study experience.

Question 13:

How many terms of G.P. 3, 32, 33, … are needed to give the sum 120?

Answer:

The given G.P. is 3, 32, 33, …

Let n terms of this G.P. be required to obtain the sum as 120.

S subscript n space equals space fraction numerator a open parentheses r to the power of n space minus space 1 close parentheses over denominator r minus 1 end fraction

Here, a = 3 and r = 3

∴ S subscript n space equals space 120 space equals space fraction numerator 3 space open parentheses 3 to the power of n space minus 1 close parentheses over denominator 3 minus 1 end fraction

rightwards double arrow 120 space equals space fraction numerator 3 open parentheses 3 to the power of n space minus 1 close parentheses over denominator 2 end fraction
rightwards double arrow fraction numerator 120 space cross times 2 over denominator 3 end fraction space equals space 3 to the power of n space minus 1
rightwards double arrow 3 to the power of n space minus 1 space equals space 80
rightwards double arrow 3 to the power of n space equals space 81
rightwards double arrow 3 to the power of n space equals space 3 to the power of 4

∴  n = 4

Thus, four terms of the given G.P. are required to obtain the sum as 120.


Study Tips for Answering NCERT Questions:

NCERT questions are designed to test your understanding of the concepts and theories discussed in the chapter. Here are some tips to help you answer NCERT questions effectively:

  • Read the question carefully and focus on the core concept being asked.
  • Reference examples and data from the chapter when answering questions about Sequence and Series.
  • Review previous year question papers to get an idea of how such questions may be framed in exams.
  • Practice answering questions within the time limit to improve your speed and accuracy.
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Comments

  • Salome
  • Jun 28, 2023

Kindly tell us what r means


  • HARISH N BIDARI
  • Feb 03, 2023

Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏


  • HARISH N BIDARI
  • Feb 03, 2023

Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏


  • Riya prasad
  • Oct 30, 2021

Very good 😁😁


  • Sameer sharma
  • Nov 04, 2019

Thanks for solving the question


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Welcome to the NCERT Solutions for Class 11 Mathematics - Chapter . This page offers a step-by-step solution to the specific question from Excercise 3 , Question 13: How many terms of G.P. 3, 32, 33, … are needed to give the sum 120?....