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 the 21 st row

Answer 1

Answer:

There are 60 seats in 21 st row

Step-by-step explanation:

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

t1 t2 t3 t21

20+22+24+........=S25

a=20

d=22-20=2

t21=a+20d

=20+20×2

=20+40

=60