Question

There are 25 rows of seats in an auditorium . The first row is of 20 seats ,the second of 22 seats, third of 24 seats, and so on . How many chairs are there in the 21st row ?

Answer 1

Given first row$=20$,second row$=22$,third rows$=24$ and so on

$20,22,24,26$

this is in an A.P

$a=20$

$d=22-20=2$

$a_n=a+(n-1)d$

$a_{21}=20+\left(20\right)2$

$=60$

There would be $60$ seats in ${21}^{st}$ row.