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

Q13.

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

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.

👍 0
👎 0
✍️ Add Answer
🚩 Report

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.
  • Discuss your answers with your teachers or peers to get feedback and improve your understanding.

Important Questions & Answers

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

The given G.P. is 3, 32, 33, …

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



Here, a = 3 and r = 3

∴ 

∴  n = 4

Thus, f...

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

Step-by-step explanation:
• The given G
• P
• is 3, 32, 33, …

• Let n terms of this G

Why is this answer important for exams?

This question is important because it tests key concepts from the NCERT syllabus and is frequently asked in CBSE exams.

Which NCERT concept is used in this question?

This question is based on core NCERT concepts explained in the chapter and should be revised thoroughly before exams.

What common mistakes should be avoided in this question?

Students often lose marks by skipping steps, writing incomplete explanations, or misunderstanding keywords used in the question.

Latest Blog Posts

Stay updated with our latest educational content and study tips

Simple and Compound Interest Formulas with Questions

Simple and Compound Interest Formulas with Questions

Interest is one of the most significant ideas in maths and financial calculations. It is very common in banking, loan applications, investments, saving account and competitive exams. Simple Interest and Compound Interest make it easier to find out how much more is earned and/or paid on a principal during the period of time. These Interest … Read more

Read More
Spoken English Course Topics for Beginners in 2026

Spoken English Course Topics for Beginners in 2026

In 2026, students, professionals, and job seekers must have a high level of spoken English. Spoken English is a beginner level course to enhance learners’ communication skills in English, their pronunciation, vocabulary, grammar structure and confidence in speaking English fluently. Today, the emphasis of spoken English courses is placed on actual conversations, everyday speech practice … Read more

Read More
Difference Between AI and Machine Learning

Difference Between AI and Machine Learning

Artificial Intelligence (AI) and Machine Learning (ML) are two of the most sought-after technologies in today’s digital era. Although these terms are often used together, they are not the same. Machine Learning is, in fact, a component of Artificial Intelligence that enables systems to learn and enhance on their own, without direct programming. AI is … Read more

Read More
Time, Speed and Distance Formulas

Time, Speed and Distance Formulas

Time, Speed, and Distance are some of the most important concepts in mathematics and aptitude. These are the concepts which are used to calculate the speed of an object, time taken for an object to move and the distance traveled during the motion. Questions from this topic are frequently seen in School Tests, Competitive Tests, … Read more

Read More

Student Discussion

Salome
Class · · , · Jun 28, 2023
Kindly tell us what r means
👍 👎 Reply
HARISH N BIDARI
Class · · , · Feb 03, 2023
Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏
👍 👎 Reply
HARISH N BIDARI
Class · · , · Feb 03, 2023
Thank you sir/medam...this answer is helpful to us...😘💐🙏🙏
👍 👎 Reply
Riya prasad
Class · · , · Oct 30, 2021
Very good 😁😁
👍 👎 Reply
Sameer sharma
Class · · , · Nov 04, 2019
Thanks for solving
the question
👍 👎 Reply

ADD NEW COMMENT

        Can’t find your school? Type full name and submit.