What will be the (13)th term of the AP (120,109,98,\ldots)?

Correct answer: -12

Here, the first term is \(a=120\) and the common difference is \(d=109-120=-11\). The \(n\)th term is given by \(a_n=a+(n-1)d\). Thus, \(a_{13}=120+(13-1)(-11)=120-132=-12\). Therefore, \(-12\) is correct. \(-10\) can result from incorrectly counting the number of differences or using \(n\) instead of \((n-1)\). Exam tip: for the \(n\)th term, always use \((n-1)\) common differences.