What is the value of (a_9+a_{11}) for the arithmetic progression (14,19,24,\ldots)?
Answer and explanation
Correct answer: 118
Here, the first term is \(a=14\) and the common difference is \(d=5\). Using \(a_n=a+(n-1)d\), we get \(a_9=14+8\times5=54\) and \(a_{11}=14+10\times5=64\). Therefore, \(a_9+a_{11}=54+64=118\). Option 124 may result from incorrectly counting the number of differences for \(a_{11}\). Exam tip: always use \((n-1)d\) for the \(n\)th term.
Frequently asked questions
What is the correct answer to this question?
118
Why is this the correct answer?
Here, the first term is \(a=14\) and the common difference is \(d=5\). Using \(a_n=a+(n-1)d\), we get \(a_9=14+8\times5=54\) and \(a_{11}=14+10\times5=64\). Therefore, \(a_9+a_{11}=54+64=118\). Option 124 may result from incorrectly counting the number of differences for \(a_{11}\). Exam tip: always use \((n-1)d\) for the \(n\)th term.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Arithmetic Progression.
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