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In an auditorium, the first row has 18 seats and each successive row has 3 more seats. Ananya says that the 15th row will have \(18+15\times3=63\) seats. Which is the correct assessment of her statement?

Answer and explanation

Correct answer: The statement is incorrect; there are 14 increases after the first row, so the answer is 60.

The 15th row is the 15th term of the AP. \(a_{15}=a+(15-1)d=18+14\times3=60\). Ananya forgot to use \(n-1\). Exam tip: count the increases after the first term, not the row number itself.

Related tags

Arithmetic ProgressionNth TermAp FormulaApplication QuestionCommon ErrorClass 10 MathematicsFinding The $N$Th Term Of An ApFinding The N Th Term Of An Ap

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