What is the (15)th term in the AP (-20,-15,-10,-5,\ldots)?
Answer and explanation
Correct answer: 50
The first term is \(a=-20\), and the common difference is \(d=-15-(-20)=5\). The \(n\)th term is given by \(a_n=a+(n-1)d\). Therefore, \(a_{15}=-20+(15-1)\times5=-20+70=50\). Hence, 50 is correct. The value 45 may result from incorrectly using 13 instead of \(n-1\). Exam tip: always use \(n-1\), not \(n\), in the nth-term formula.
Frequently asked questions
What is the correct answer to this question?
50
Why is this the correct answer?
The first term is \(a=-20\), and the common difference is \(d=-15-(-20)=5\). The \(n\)th term is given by \(a_n=a+(n-1)d\). Therefore, \(a_{15}=-20+(15-1)\times5=-20+70=50\). Hence, 50 is correct. The value 45 may result from incorrectly using 13 instead of \(n-1\). 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.
Student feedback
Was this question useful?
👍 0 Helpful 👎 0 Not helpful
Yes 0% No 0%
0 responsesStudent Reviews
No published reviews yet.
