What is the (18)th term of the AP (-15,-9,-3,3,\ldots)?
Answer and explanation
Correct answer: \(87\)
The first term is \(a=-15\) and the common difference is \(d=-9-(-15)=6\). The \(n\)th term is given by \(a_n=a+(n-1)d\). Therefore, \(a_{18}=-15+(18-1)\times6=-15+102=87\). Hence, \(87\) is correct. A close error such as \(85\) can result from incorrectly counting the number of common differences. Exam tip: always use \(n-1\) common differences to find the \(n\)th term of an AP.
Frequently asked questions
What is the correct answer to this question?
\(87\)
Why is this the correct answer?
The first term is \(a=-15\) and the common difference is \(d=-9-(-15)=6\). The \(n\)th term is given by \(a_n=a+(n-1)d\). Therefore, \(a_{18}=-15+(18-1)\times6=-15+102=87\). Hence, \(87\) is correct. A close error such as \(85\) can result from incorrectly counting the number of common differences. Exam tip: always use \(n-1\) common differences to find the \(n\)th term of an AP.
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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
