Question

An auditorium has 45 rows, with 24 seats in first row and and 4 more seats in each row thereafter. How many seats are there in last row?

Answer 1

The list of number of seats in each row starting with the first row is :

24, 24 + 4, 24 + 4 + 4, ..............

that is 24, 28, 32,.....................

The above list forms an AP with first term, a = 28 and the common difference, d = 4

number of rows, n = 45

Let the number of seats in the 45^th row = a_n

now, a_n = a + (n - 1)d = 24 + (45 - 1)4 = 24 + 44 × 4 = 24 + 176 = 200

so the number of seats in the last row = 200