Question

There are 25 rows of seats in an auditorium the 1st row is of 20 seats the 2nd row of 22 seats the 3rd row of 24 seats and so on .how many seats are there in 21st row

Answer 1

T1=20,T2=22,T3=24.

D=22-20=24-22=2

Therefore 20,22,24.... is an A.P

We have a=20,d=2.

tn= a+(n-1)d

T21=20+(21-1)×2

=20+20×2

=20+40

=60seats

Therefore there are 60 seats in the 21st row

Answer 2

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!