What will be the sum of the first (10) terms of the AP (7,14,21,\ldots)?
Answer and explanation
Correct answer: 385
Here, the first term is \(a=7\), the common difference is \(d=7\), and \(n=10\). The tenth term is \(a_{10}=7+(10-1)\times7=70\). Therefore, \(S_{10}=\frac{10}{2}(7+70)=5\times77=385\). Hence, 385 is the correct option. Choosing 365 would result from using an incorrect number of terms or last term. Exam tip: identify \(a\), \(d\), \(n\), and the last term before applying the sum formula.
Frequently asked questions
What is the correct answer to this question?
385
Why is this the correct answer?
Here, the first term is \(a=7\), the common difference is \(d=7\), and \(n=10\). The tenth term is \(a_{10}=7+(10-1)\times7=70\). Therefore, \(S_{10}=\frac{10}{2}(7+70)=5\times77=385\). Hence, 385 is the correct option. Choosing 365 would result from using an incorrect number of terms or last term. Exam tip: identify \(a\), \(d\), \(n\), and the last term before applying 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.
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