The first term of an AP is (25) and the common difference is (4). What will be the (21)st term?
Answer and explanation
Correct answer: 105
For an arithmetic progression, the formula is \(a_n=a_1+(n-1)d\). Here, \(a_1=25\), \(d=4\), and \(n=21\). Thus, \(a_{21}=25+(21-1)\times4=25+80=105\). Therefore, the correct answer is 105. Remember to multiply the common difference by \(n-1\), not by \(n\); this is why 109 is incorrect.
Frequently asked questions
What is the correct answer to this question?
105
Why is this the correct answer?
For an arithmetic progression, the formula is \(a_n=a_1+(n-1)d\). Here, \(a_1=25\), \(d=4\), and \(n=21\). Thus, \(a_{21}=25+(21-1)\times4=25+80=105\). Therefore, the correct answer is 105. Remember to multiply the common difference by \(n-1\), not by \(n\); this is why 109 is incorrect.
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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