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Question
There is an auditorium with 35 rows of seats. There are 20 seats in the first row, 22 seats in the second row, 24 seats in the third row and so on. Find the number of seats in the twenty-fifth row.
Solution
Number of seats in the first row = 20
a = 20
Increase in the number of seats in consecutive rows = 2
d = 2
To find the number of seats in the 25th row, find t25
tn = a + (n – 1)d ... (Formula)
∴ t25 = 20 + (25 – 1) x 2 ... (Substituting the values)
= 20 + (24 x 2)
= 20+48
∴ t25 = 68
Thus, the number of seats in the twenty-fifth row is 68.
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