What is the (28)th term of the AP (9,15,21,27,\ldots)?
Answer and explanation
Correct answer: 171
For this AP, the first term is \(a=9\) and the common difference is \(d=15-9=6\). The \(n\)th term is \(a_n=a+(n-1)d\). Therefore, \(a_{28}=9+(28-1)\times6=9+162=171\). Hence, 171 is correct. Getting 169 usually indicates an arithmetic error while adding \(27\times6\). Exam tip: always use \(n-1\), not \(n\), in the nth-term formula.
Frequently asked questions
What is the correct answer to this question?
171
Why is this the correct answer?
For this AP, the first term is \(a=9\) and the common difference is \(d=15-9=6\). The \(n\)th term is \(a_n=a+(n-1)d\). Therefore, \(a_{28}=9+(28-1)\times6=9+162=171\). Hence, 171 is correct. Getting 169 usually indicates an arithmetic error while adding \(27\times6\). Exam tip: always use \(n-1\), not \(n\), in the nth-term formula.
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.
