The first term of an AP is (25) and the (18)th term is (93). What is the common difference?
Answer and explanation
Correct answer: 4
For an AP, the nth-term formula is \(a_n=a+(n-1)d\). Here, \(93=25+(18-1)d\), so \(93=25+17d\). Thus, \(68=17d\) and \(d=4\). If the common difference were 3, the 18th term would be \(25+17\times3=76\), not 93. Exam tip: use \(n-1\), not n, in the nth-term formula.
Frequently asked questions
What is the correct answer to this question?
4
Why is this the correct answer?
For an AP, the nth-term formula is \(a_n=a+(n-1)d\). Here, \(93=25+(18-1)d\), so \(93=25+17d\). Thus, \(68=17d\) and \(d=4\). If the common difference were 3, the 18th term would be \(25+17\times3=76\), not 93. Exam tip: 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.
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