If the first term of an AP is (9) and the common difference is (10), what is the (7)th term?
Answer and explanation
Correct answer: 69
The formula for the nth term of an AP is \(a_n=a+(n-1)d\). Here, \(a=9\), \(d=10\), and \(n=7\), so \(a_7=9+(7-1)\times10=9+60=69\). Hence, 69 is correct. The answer 79 would result from incorrectly adding \(7d\); only six common differences are added to reach the seventh term. Exam tip: always use \((n-1)\), not \(n\), in the nth-term formula.
Frequently asked questions
What is the correct answer to this question?
69
Why is this the correct answer?
The formula for the nth term of an AP is \(a_n=a+(n-1)d\). Here, \(a=9\), \(d=10\), and \(n=7\), so \(a_7=9+(7-1)\times10=9+60=69\). Hence, 69 is correct. The answer 79 would result from incorrectly adding \(7d\); only six common differences are added to reach the seventh term. Exam tip: always 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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