For an arithmetic progression with (a=15) and (a_8=71), what is (d)?
Answer and explanation
Correct answer: \(8\)
Use the AP formula \(a_n=a+(n-1)d\). Thus, \(a_8=15+(8-1)d=15+7d\). Since \(a_8=71\), \(71=15+7d\), so \(7d=56\) and \(d=8\). Do not choose \(7\): there are seven common differences from the first term to the eighth term. Exam tip: write \((n-1)\) explicitly before substituting values in the AP formula.
Frequently asked questions
What is the correct answer to this question?
\(8\)
Why is this the correct answer?
Use the AP formula \(a_n=a+(n-1)d\). Thus, \(a_8=15+(8-1)d=15+7d\). Since \(a_8=71\), \(71=15+7d\), so \(7d=56\) and \(d=8\). Do not choose \(7\): there are seven common differences from the first term to the eighth term. Exam tip: write \((n-1)\) explicitly before substituting values in the AP formula.
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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