Quantitative Aptitude – Modern Maths – Sequence and Series – The value of the sum 7 x 11

Quantitative Aptitude – Modern Maths - Sequence and Series – The value of the sum 7 x 11

Slot -2 – Quantitative Aptitude – Modern Maths – Sequence and Series – The value of the sum 7 x 11

The value of the sum 7 x 11 + 11 x 15 + 15 x 19 + …+ 95 x 99 is?

a) 80707

b) 80730

c) 80773

d) 80751

Answer: a) 80707

Solution: 7 x 11 + 11 x 15 + 15 x 19 + …+ 95 x 99

nth term of series = {4(n+1)-1}×{ 4 (n+1)+3}=16n^2+16+32n+8n+8-

3=16n^2+40n+21

Thus 7 x 11 + 11 x 15 + 15 x 19 + …+ 95 x 99 = ∑ Tn=∑ (16n^2+40n+15)

Required sum = ∑ Tn=∑ (16n^2+ 40n+15)=16 ×(n(n+1(2n+1))/6 + 40×n(n+1)/2 + 21n

Putting n= 23

Sum = 16×23×24×47/6+40×23×24/2+21×23

=69184+11040+483=80707

Correct option a) 80707

Other posts related to Quantitative Aptitude – Modern Maths

Permutation and Combination – Fundamental Principle of Counting
Permutation and Combination – Distribution of Objects
How to find Rank of a Word in Dictionary (With or Without Repetition)
Set Theory- Maximum and Minimum Values
How to solve questions based on At least n in Set Theory for CAT Exam?
Sequence and Series Problems and Concepts for CAT 2017 Exam Preparation
Basic Probability Concepts for CAT Preparation

Online Coaching Course for CAT Exam Preparation

a) 750+ Videos covering entire CAT syllabus
b) 2 Live Classes (online) every week for doubt clarification
c) Study Material & PDFs for practice and understanding
d) 10 Mock Tests in the latest pattern
e) Previous Year Questions solved on video

Know More about Online CAT Course

Leave a Reply

Your email address will not be published.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