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There Are 25 Rows of Seats in an Auditorium. the First Row is of 20 Seats, the Second of 22 Seats, the Third of 24 Seats, and So On. How Many Chairs Are There in the 21st Row ? - Algebra

Question

There are 25 rows of seats in an auditorium. The first row is of 20 seats, the second of 22 seats, the third of 24 seats, and so on. How many chairs are there in the 21st row ?

Solution

The arrangement of chairs is 20, 22, 24, 26, ..........
Which  is an A. P.
Here, a = 20, d = 2. We want to find t21
tn = a + (n-1)d
∴ t21 = 20 + (21-1) × 2
          = 20 + 40
          = 60
∴  There are 60 chairs in the 21st row. 

  Is there an error in this question or solution?
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There Are 25 Rows of Seats in an Auditorium. the First Row is of 20 Seats, the Second of 22 Seats, the Third of 24 Seats, and So On. How Many Chairs Are There in the 21st Row ? Concept: Sum of First n Terms of an AP.
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