Find the sum of the first (15) terms of the AP (4,8,12,\ldots).
Answer and explanation
Correct answer: 480
Here, the first term is \(a=4\), the common difference is \(d=4\), and \(n=15\). Using \(S_n=\frac{n}{2}[2a+(n-1)d]\), we get \(S_{15}=\frac{15}{2}[2(4)+14(4)]=\frac{15}{2}(64)=480\). Therefore, 480 is correct. A value such as 420 can result from using the wrong number of terms or last term. Exam tip: write down \(a\), \(d\), and \(n\) before applying the AP sum formula.
Frequently asked questions
What is the correct answer to this question?
480
Why is this the correct answer?
Here, the first term is \(a=4\), the common difference is \(d=4\), and \(n=15\). Using \(S_n=\frac{n}{2}[2a+(n-1)d]\), we get \(S_{15}=\frac{15}{2}[2(4)+14(4)]=\frac{15}{2}(64)=480\). Therefore, 480 is correct. A value such as 420 can result from using the wrong number of terms or last term. Exam tip: write down \(a\), \(d\), and \(n\) before applying the AP 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.
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