If (a=13), (d=6), and (a_n=121), what is the value of (n)?
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Answer and explanation
Correct answer: 19
The formula for the nth term of an AP is \(a_n=a+(n-1)d\). Substituting the given values gives \(121=13+(n-1)\times6\). Thus, \(108=6(n-1)\), so \(n-1=18\) and \(n=19\). Option 18 is the value of \(n-1\), not of n. Exam tip: always add 1 after finding \(n-1\).
Frequently asked questions
What is the correct answer to this question?
19
Why is this the correct answer?
The formula for the nth term of an AP is \(a_n=a+(n-1)d\). Substituting the given values gives \(121=13+(n-1)\times6\). Thus, \(108=6(n-1)\), so \(n-1=18\) and \(n=19\). Option 18 is the value of \(n-1\), not of n. Exam tip: always add 1 after finding \(n-1\).
Which subject and chapter does this question cover?
This is a Class 10 Mathematics question. Chapter: Arithmetic Progressions (AP). Topic: Finding the $n$th term of an AP.
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