What is the sum of the first (8) terms of the AP (20,18,16,\ldots)?
Answer and explanation
Correct answer: 104
For this AP, the first term is \(a=20\), the common difference is \(d=-2\), and \(n=8\). Using \(S_n=\frac{n}{2}[2a+(n-1)d]\), we get \(S_8=\frac{8}{2}[2(20)+7(-2)]=4(40-14)=104\). Therefore, the correct answer is 104. An option such as 108 can result from not handling the negative common difference correctly. Exam tip: identify \(a\), \(d\), and \(n\) before substituting in the sum formula.
Frequently asked questions
What is the correct answer to this question?
104
Why is this the correct answer?
For this AP, the first term is \(a=20\), the common difference is \(d=-2\), and \(n=8\). Using \(S_n=\frac{n}{2}[2a+(n-1)d]\), we get \(S_8=\frac{8}{2}[2(20)+7(-2)]=4(40-14)=104\). Therefore, the correct answer is 104. An option such as 108 can result from not handling the negative common difference correctly. Exam tip: identify \(a\), \(d\), and \(n\) before substituting in the sum formula.
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the sum of the first $n$ terms of an AP.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
