If (a=5) and (d=-1), find the (20)th term of the AP.
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Answer and explanation
Correct answer: -14
The nth term of an AP is \(a_n=a+(n-1)d\). Thus, \(a_{20}=5+(20-1)(-1)=5-19=-14\). Therefore, \(-14\) is correct. The value \(-13\) would result from incorrectly using 18 in place of \(n-1\). Exam tip: always multiply the common difference by \(n-1\) when finding the nth term.
Frequently asked questions
What is the correct answer to this question?
-14
Why is this the correct answer?
The nth term of an AP is \(a_n=a+(n-1)d\). Thus, \(a_{20}=5+(20-1)(-1)=5-19=-14\). Therefore, \(-14\) is correct. The value \(-13\) would result from incorrectly using 18 in place of \(n-1\). Exam tip: always multiply the common difference by \(n-1\) when finding the nth term.
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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