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Class 10MathematicsArithmetic Progressions (AP)Word problems based on APsMedium
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An auditorium has 20 seats in the first row, and each successive row has 4 more seats than the preceding row. What is the total number of seats in the first 15 rows?

Answer and explanation

Correct answer: 720

This is an AP with \(a=20\), \(d=4\), and \(n=15\). \(S_{15}=\frac{15}{2}[2(20)+14(4)]=\frac{15}{2}(96)=720\). Finding only the 15th-row seats would not give the total. In exams, remember to use \(n-1\) in the sum formula.

Related tags

Arithmetic ProgressionAp Word ProblemsSum Of ApClass 10 MathematicsAuditorium SeatingWord Problems Based On ApsArithmetic Progressions (Ap)Arithmetic Progressions Ap
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