What is the sum of the first (14) terms of the arithmetic progression (11,18,25,\ldots)?
Answer and explanation
Correct answer: 791
Here, the first term is \(a=11\), the common difference is \(d=18-11=7\), and \(n=14\). The sum of the first \(n\) terms is \(S_n=\frac{n}{2}[2a+(n-1)d]\). Thus, \(S_{14}=\frac{14}{2}[2(11)+13(7)]=7(22+91)=7\times113=791\). Therefore, the correct answer is 791. A value such as 773 usually results from an error in using \((n-1)d\) or in multiplication. Exam tip: write down \(a\), \(d\), and \(n\) separately before applying the sum formula.
Frequently asked questions
What is the correct answer to this question?
791
Why is this the correct answer?
Here, the first term is \(a=11\), the common difference is \(d=18-11=7\), and \(n=14\). The sum of the first \(n\) terms is \(S_n=\frac{n}{2}[2a+(n-1)d]\). Thus, \(S_{14}=\frac{14}{2}[2(11)+13(7)]=7(22+91)=7\times113=791\). Therefore, the correct answer is 791. A value such as 773 usually results from an error in using \((n-1)d\) or in multiplication. Exam tip: write down \(a\), \(d\), and \(n\) separately before applying the sum formula.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Arithmetic Progression.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
