Find the sum of the first (11) terms of the AP (0,4,8,\ldots).
Answer and explanation
Correct answer: 220
Here, the first term is \(a=0\), the common difference is \(d=4\), and \(n=11\). The 11th term is \(a_{11}=a+(n-1)d=0+10\times4=40\). Hence, \(S_{11}=\frac{n}{2}(a+l)=\frac{11}{2}(0+40)=220\). The value \(240\) can result from counting the terms or the last term incorrectly. Exam tip: before using the sum formula, use \(n-1\) while finding the \(n\)th term.
Frequently asked questions
What is the correct answer to this question?
220
Why is this the correct answer?
Here, the first term is \(a=0\), the common difference is \(d=4\), and \(n=11\). The 11th term is \(a_{11}=a+(n-1)d=0+10\times4=40\). Hence, \(S_{11}=\frac{n}{2}(a+l)=\frac{11}{2}(0+40)=220\). The value \(240\) can result from counting the terms or the last term incorrectly. Exam tip: before using the sum formula, use \(n-1\) while finding the \(n\)th term.
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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