If (a=12) and (d=9), what is the value of (a_5+a_8)?
Answer and explanation
Correct answer: 123
The nth term of an arithmetic progression is \(a_n=a+(n-1)d\). Thus, \(a_5=12+(5-1)\times9=48\) and \(a_8=12+(8-1)\times9=75\). Therefore, \(a_5+a_8=48+75=123\). A value such as 117 may result from counting the common difference incorrectly. Exam tip: write \(n-1\) first while finding each term, then add the terms.
Frequently asked questions
What is the correct answer to this question?
123
Why is this the correct answer?
The nth term of an arithmetic progression is \(a_n=a+(n-1)d\). Thus, \(a_5=12+(5-1)\times9=48\) and \(a_8=12+(8-1)\times9=75\). Therefore, \(a_5+a_8=48+75=123\). A value such as 117 may result from counting the common difference incorrectly. Exam tip: write \(n-1\) first while finding each term, then add the terms.
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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