If (a_8=66) and (a=17), what is (d)?
Answer and explanation
Correct answer: \(7\)
In an arithmetic progression, \(a_n=a+(n-1)d\). Therefore, \(a_8=a+7d\). Substituting the given values gives \(66=17+7d\), so \(7d=49\) and \(d=7\). Hence, option C is correct. If \(d=8\), the eighth term would be \(17+7\times8=73\), not 66. Exam tip: use \(n-1\), not \(n\), in the formula for the \(n\)th term.
Frequently asked questions
What is the correct answer to this question?
\(7\)
Why is this the correct answer?
In an arithmetic progression, \(a_n=a+(n-1)d\). Therefore, \(a_8=a+7d\). Substituting the given values gives \(66=17+7d\), so \(7d=49\) and \(d=7\). Hence, option C is correct. If \(d=8\), the eighth term would be \(17+7\times8=73\), not 66. Exam tip: use \(n-1\), not \(n\), in the formula for the \(n\)th term.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: Arithmetic Progression.
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