Question

there are 25 row of seat in an Auditorium the First row is the 20 seat and second of 22 seat 3rd row of 24 seat and so on how many chairs and there in the 21st floor

Answer 1

it's an AP bro 20,22,24...........nth terms

An= a + (n-1)d. A21= 20+20(2)

answer is 60 seats

Answer 2

Answer: 60.  

Step-by-step explanation:

The number of seats will be in the following order-

20, 22, 24,.........

It clearly forms an arithmetic sequence.

From the question, you have

a= 20 (first term), d= 2 (common diff)

n=21 (asked) , t21=?

The formula of general term is  

tn = a+(n-1)d

t21 = 20+(21-1)2

= 20+ (20)2

= 20+40

= 60.

Hope I helped you!