Question

How can you find the number of seats in the succeding rows?

Answer 1

By using Arithmetic progression.

For example - first row has $15$ seats, second row has $18$ seats and third row has $21$ seats and so on.

So we can see a constant rise in number of seats called common difference that is $d= 3.$

Seats in first row $a_1= 15$

We can find seats in $n^{th}$ row by using the formula $a_n= a_1 +(n-1) d$

To find seats in $5th$ row, $n= 5.$

So seats in fifth row are

$a_5= a_1+ (n-1)d= 15+(5-1)3=27$