If \(a_n=\frac{n(n+5)}{3}\), what is the value of \(a_{12}\)?
Answer and explanation
Correct answer: 68
Substitute \(n=12\) into \(a_n=\frac{n(n+5)}{3}\): \(a_{12}=\frac{12(12+5)}{3}=\frac{12\times17}{3}=4\times17=68\). Hence, 68 is correct. The distractor 66 can result from incorrectly adding \(12+5\). In an exam, substitute the term number first and then simplify systematically.
Frequently asked questions
What is the correct answer to this question?
68
Why is this the correct answer?
Substitute \(n=12\) into \(a_n=\frac{n(n+5)}{3}\): \(a_{12}=\frac{12(12+5)}{3}=\frac{12\times17}{3}=4\times17=68\). Hence, 68 is correct. The distractor 66 can result from incorrectly adding \(12+5\). In an exam, substitute the term number first and then simplify systematically.
Which subject and chapter does this question cover?
This is a Class 9 Mathematics question. Chapter: Sequences and Progressions. Topic: nth term.
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