If in an AP (a_{18}=130) and (d=8), what is (a_4)?
Answer and explanation
Correct answer: 18
For two terms of an AP, \(a_{18}=a_4+(18-4)d\). Therefore, \(a_4=130-14\times 8=130-112=18\). Hence, 18 is correct. Option 20 is close, but adding 14 common differences to it gives \(a_{18}=132\), not 130. Exam tip: to find an earlier term from a later term, subtract the position gap multiplied by \(d\).
Frequently asked questions
What is the correct answer to this question?
18
Why is this the correct answer?
For two terms of an AP, \(a_{18}=a_4+(18-4)d\). Therefore, \(a_4=130-14\times 8=130-112=18\). Hence, 18 is correct. Option 20 is close, but adding 14 common differences to it gives \(a_{18}=132\), not 130. Exam tip: to find an earlier term from a later term, subtract the position gap multiplied by \(d\).
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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